Shilling attacks pose a significant threat to the integrity and reliability of recommender systems by injecting fake user profiles to promote or demote targeted items. Existing generative approaches often suffer from unstable training dynamics and limited realism in the synthesized profiles. In this paper, we propose PGAN, a novel Penalized Generative Adversarial Network enhanced with latent space perturbations to generate high-quality, diverse, and undetectable shilling attack profiles. PGAN incorporates a gradient penalty to stabilize discriminator training and applies controlled noise perturbations in the generator's latent space to improve robustness and attack diversity. We evaluate PGAN on real-world datasets and demonstrate that it consistently outperforms traditional statistical attacks and baseline GAN-based models across multiple evaluation metrics, including Hit Ratio@K, Prediction Shift, and attack success rate. Experimental results also confirm the realism of the generated profiles through similarity analysis with genuine users. Our proposed model outperforms traditional and state-of-the-art methods, achieving HR@10 scores of 0.2051 and 0.2076 on the MovieLens and Amazon datasets, respectively.

Recommendation systems have proved to be a compelling performance in overcoming the data overload problem in many domains, such as e-commerce, e-health, and transportation. Recommender systems guide users/clients to personalized recommendations based on their preferences. However, some recommendation systems are vulnerable to shilling attacks, which create rating biases or fake reviews that will eventually affect the authenticity and integrity of the generated recommendations. This survey comprehensively covers various shilling attack methods, including high-knowledge, low-knowledge attacks, and obfuscated attacks. It explores malicious review generators that generate fake text. In addition to that, this survey covers shilling attack detection methods such as supervised, unsupervised, semisupervised, and hybrid techniques. Natural Language Processing techniques are also thoroughly explored for fake text review detection using large language models (LLMs). A wide range of detection mechanisms incorporated in the literature is examined, such as convolutional neural network (CNN), long short term memory (LSTM)-based detectors for rating-based shilling attacks, and bidirectional encoder representation (BERT) and RoBERTa-based detectors for fake reviews that are accompanied by shilling attacks, aiming to offer insights into the evolving methods of shilling attack strategies and the corresponding advancements in the detection methods.

Recommender systems (RS) are integral to modern e-commerce and content platforms. Yet, their reliance on user-item interaction data makes them vulnerable to shilling attacks, where fake data is injected to manipulate recommendations. Traditional shilling attack strategies utilize basic statistical properties of user-item data to create deceptive profiles. Still, recent advancements have shifted towards model-based attacks leveraging machine learning to enhance effectiveness and evade detection. This paper introduces GraphAush, a novel neural shilling attack model that employs Generative Adversarial Networks (GANs) with a novel generator shilling loss tailored to manipulate the user-item interaction graph. By incorporating a novel generator shilling loss function that leverages Node2Vec embeddings, GraphAush optimizes fake profile generation to maximize the effectiveness of attacks while minimizing detectability. This method overcomes the limitations of previous models, which either require intricate knowledge of the target RS or use indirect graph-based approaches. The efficacy of GraphAush was validated through experiments with multiple benchmark datasets, revealing its strong performance against traditional heuristic and other GAN-based attack methods. This innovative approach highlights a significant advancement in adversarial techniques for RS and sets a new benchmark for evaluating shilling attack strategies.

This research paper presents a comprehensive study on applying deep learning models for optimizing power balance management in smart grids. Utilizing a synthetic dataset based on a 4-node star network, this paper explores the efficacy of a deep learning model augmented to 60,000 observations, reflecting permutations of consumer nodes. The model incorporates advanced data preprocessing techniques, including feature selection, normalization, and outlier removal, alongside sophisticated machine learning strategies like Bayesian Optimization for hyperparameter tuning. The core of the research lies in evaluating the model's performance and resilience. The model was rigorously tested against various data loss scenarios using different imputation methods and assessed through metrics like accuracy, BCE Loss, and MSE Loss. These evaluations provided insights into the model's robustness and adaptability in simulating grid stability and resilience conditions.

Context-aware recommendation systems (CARSs) leverage contextual information, e.g., time, location, or mood, to generate more personalized recommendations with high accuracy; however, existing CARSs fall short in: 1) handling the high sparsity of data; 2) designing scalable solutions in real time; and 3) providing more personalized solutions with the current limited static contexts. This article proposes a multi-CARS based on consensus clustering (MCARS-CC) to solve these challenges. The item-based contextual information is acquired using explicit static and inferred contexts by applying sentiment analysis to the users’ reviews. The proposed model is experimented using contextual prefiltering and postfiltering techniques applied to two benchmark datasets, Yelp and TripAdvisor. The model is evaluated using mean absolute error (MAE), root-mean-squared error (RMSE), response time, precision, recall, and F-measure. The experimental results show that the proposed MCARS-CC model outperforms other baseline techniques using the accuracy and error-based metrics. Incorporating hypergraph partitioning algorithm (HGPA) could improve the MAE and RMSE by 25.96% and 8.94% (Yelp), respectively. Also, HGPA led to an 18.47% and 15.94% improvement ratio in terms of MAE and RMSE (TripAdvisor), respectively.

Customers use reviews as a primary source of information to judge a product or service. Positive reviews help boost companies’ reputations, increasing their revenue by attracting new clients, and increasing the purchasing order size. On the other hand, negative reviews significantly reduce sales, which might be the case due to competitive advantage. Organizations can use fake (i.e., misleading or fraudulent) reviews to generate fast profits by deceiving customers into buying their products. Recently, various methods to assess the legitimacy of reviews have been introduced using advances in machine learning. However, existing methods fall short of achieving highly accurate detection results for unbalanced classes. We aimed to create a spam review identification model using ensemble-based learning while balancing classes using sampling techniques. This article proposes a weighted stacking ensemble model with sampling (WSEM-S) for efficient fake reviews detection. We used$n$-gram models to effectively model language data for feature retrieval. The experimental results on three customer reviews datasets: YELPNYC, Deceptive Opinion Spam Corpus (DOSC) v1.4, and Deception datasets show that the proposed model outperforms the conventional machine learning techniques [Naïve Bayes, logistic regression, K-nearest neighbor (KNN), random forest, extreme gradient boosting (XGBoost), and convolutional neural network (CNN)] as well as the state-of-the-art ensemble models.

In the realm of social network analysis and mining, recommendation systems have become indispensable algorithms in assisting users and industries in navigating the available contents or products in various domains and getting the most personalized recommendations to their interests and preferences. However, if the input data has been generated by malicious users, that poses a significant challenge to recommender systems' reliability and efficiency. One of the main threats that poses a challenge to recommender systems is shilling attacks. Shilling attacks tend to manipulate or poison the data in the systems' training phase, leading to biased or compromised recommendations. To address this challenge, we propose a robust recommender system using variational autoencoders (VAE) with Anomaly detection. Our model learns complex and non-linear patterns by exclusively focusing on the user-item interaction data, represented by a binary user-item interaction matrix, making it more resilient to classic shilling attacks. Moreover, our paper incorporates an anomaly detection mechanism, alongside the autoencoder, that analyzes the reconstruction errors, i.e. (MSE) between the original interactions and their reconstructed ones. We test the model on a real-world dataset and evaluate it using Recall@k and NDCG@k. This work enhances the trustworthiness and accuracy of recommendation algorithms, mainly when deployed in social network analysis and mining, where the potential for malicious data manipulation is a critical concern.

Various digital data sets that encode user-item relationships contain a multilevel overlapping cluster structure. The user-item relation can be encoded in a weighted bipartite graph and uncovering these overlapping coclusters of users and items at multiple levels in the bipartite graph can play an important role in analyzing user-item data in many applications. For example, for effective online marketing, such as placing online ads or deploying smart online marketing strategies, identifying co-occurring clusters of users and items can lead to accurately targeted advertisements and better marketing outcomes. In this paper, we propose fast algorithms inspired by algebraic multigrid methods for finding multilevel overlapping cocluster structures of feature matrices that encode user-item relations. Starting from the weighted bipartite graph structure of the feature matrix, the algorithms use agglomeration procedures to recursively coarsen the bipartite graphs that represent the relations between the coclusters on increasingly coarser levels. New fast coarsening routines are described that circumvent the bottleneck of all-to-all similarity computations by exploiting measures of direct connection strength between row and column variables in the feature matrix. Providing accurate coclusters at multiple levels in a manner that can scale to large data sets is a challenging task. In this paper, we propose heuristic algorithms that approximately and recursively minimize normalized cuts to obtain coclusters in the aggregated bipartite graphs on multiple levels of resolution. Whereas the main novelty and focus of the paper lies in algorithmic aspects of reducing computational complexity to obtain scalable methods specifically for large rectangular user-item matrices, the algorithmic variants also define several new models for determining multilevel coclusters that we justify intuitively by relating them to principles that underlie collaborative filtering methods for user-item relationships. Experimental results show that the proposed algorithms successfully uncover the multilevel overlapping cluster structure for artificial and real data sets. Summary of Contribution: This paper develops new and efficient computational methods for finding the multilevel overlapping cocluster structure of feature matrices that encode user-item relationships. We base our approach on the use of pairwise similarity measures between features, seeking clusters of points that are similar to each other and dissimilar from the points outside the cluster. We approximately solve the problem of finding optimal overlapping coclusters on multiple levels by employing a framework that is based on efficient multilevel methods that have been used previously to solve sparse linear systems and to cluster graphs. Our main contribution is that we extend these methods in efficient manners to find coclusters in the bipartite graphs that encode common and important user-item relationships or social network relations. The novel methods that we propose are inherently scalable to large problem sizes and are naturally able to uncover overlapping coclusters at multiple levels, whereas existing methods generally only find coclusters at the fine level. We illustrate the algorithm and its performance on some standard test problems from the literature and on a proof-of-concept real-world data set that relates LinkedIn users to their skills and expertise.

The ability to predict the stock trend is one of the most challenging goals for today's traders. The successful prediction of a stock's future trend could yield significant profit. Various machine learning and deep learning have been introduced in the last decades. However, the trade-off between performance and computational complexity was not addressed. This paper aims to find a well-suited model to predict the stock market price trend, with increment in profit gain in Long and Short trading with comparable prediction performance and computational time. A state-of-art machine and deep learning methods have been investigated along with efficient feature engineering. Experimental results show that Feed Forward Neural Network (FFNN) has the best profitability performance (return) and a reasonable running time, among other tested models.

Clustering techniques are helpful in understanding gene regulation, cellular processes, and subtypes of cells. A major thrust of gene expression analysis over the last twenty years has been the acquisition of enormous amount of various distributed sources of gene expression datasets. Thus, it is becoming increasingly important to perform clustering of distributed data in-place, without the need to pool it first into a central node. The general goal of distributed clustering is achieving a level of speedup than the centralized approaches. A recent study shows that centralized cooperative clustering outperforms the non-cooperative centralized clustering approaches. In this paper a novel distributed cooperative partitional-divisive clustering in a peer-to-peer network is presented. The distributed CPDC approach is based on intermediate cooperation between the Partitional k-means and the divisive bisecting k-means in a distributed Peer-to-Peer network to produce better global solutions. Computational experiments were conducted to test the performance of the distributed CPDC approach using different gene expression datasets. Undertaken experimental results show that the performance of the distributed CPDC method is better than that of the non-cooperative distributed k-means and distributed bisecting k-means. Thus a new cooperative technique for distributed gene expression repositories is efficiently presented to discover regularities and genes that may span multiple nodes.

Clustering techniques organize a collection of objects into cohesive groups called clusters such that objects in the same cluster are more similar to each other than objects in different clusters. There are many clustering approaches proposed in the literature with different quality/complexity tradeoffs. Combining multiple clustering is an approach to overcome the deficiency of single algorithms and further enhance their performances. Current approaches to combining multiple clusterings use end-result cooperation (e.g. ensemble clustering and hybrid clustering) between the clustering algorithms. Inherent drawbacks of the end-result cooperation are: the computational complexity of ensemble clustering and the idle wasted time in the hybrid approaches. In this paper, the k-means and the bisecting k-means clustering algorithms are both combined using intermediate-cooperation strategy for the aim of obtaining better clustering solutions than non-cooperative algorithms. Undertaken experimental results show that the quality of the clustering solutions obtained from the cooperative partitional-divisive clustering (CPDC) model is better than those obtained from the non-cooperative algorithms over a number of gene expression datasets.

Data clustering plays an important role in many disciplines, where there is a need to learn the inherent grouping structure of the data in an unsupervised manner. It is well known that no clustering method can adequately handle all sorts of cluster structures and properties (e.g. shape, size, overlapping, and density). Combining multiple clustering methods is an approach to overcome the deficiency of single algorithms and further enhance their performances. Current approaches to multiple clusterings use ensemble clustering to generate aggregated solution from multiple clusterings or using a hybrid cascaded refinement to enhance the end-result clusters produced by a former clustering algorithm(s). A disadvantage of the cluster ensemble is the highly computational load of combing the clustering results especially for large and high dimensional datasets. A drawback of the hybrid approaches is that, one (or more) of the clustering algorithms stays idle until the previous algorithm(s) finishes its clustering. In this paper we propose a Cooperative Hard-Fuzzy Clustering (CHFC) model based on intermediate cooperation between the hard c-means (KM) andfuzzyc-means (FCM) to produce better clustering solutions. Our experimental results over artificial, real, and text documents datasets show that the quality of the clustering solutions obtained from the CHFC model is better than those obtained from both the KM and the FCM and also better than those obtained from hybrid cascaded models.