Web and mobile systems show constant distribution shifts due to the evolvement of services, users, and threats, severely degrading the performance of threat detection models trained on prior distributions. Fast model adaptation with minimal new data is essential for maintaining reliable security measures. A key challenge in this context is the lack of ground truth, which undermines the ability of existing solutions to align classes across shifted distributions. Moreover, the limited new data often fails to represent the underlying distribution, providing sparse and potentially noisy information for adaptation. In this paper, we propose REACT, a novel framework that adapts the model using a few unlabeled data and contextual insights. We leverage the inherent data imbalance in threat detection and meta-train weights on diverse unlabeled subsets to generalize common patterns across distributions, eliminating the reliance on labels for alignment. REACT decomposes a neural network into two complementary components: meta weights as a shared foundation of general knowledge, and residual adaptive weights as adjustments for specific shifts. To compensate for the limited availability of new data, REACT trains a hypernetwork to predict adaptive weights based on data and contextual information, enabling knowledge sharing across distributions. The meta weights and the hypernetwork are updated alternately, maximizing both generalization and adaptability. Extensive experiments across multiple datasets and models demonstrate that REACT improves AUROC by 14.85% over models without adaptation, outperforming the state-of-the-art.

Reconstructing 3D MR volumes from multiple motion-corrupted stacks of 2D slices has shown promise in imaging of moving subjects, e. g., fetal MRI. However, existing slice-to-volume reconstruction methods are time-consuming, especially when a high-resolution volume is desired. Moreover, they are still vulnerable to severe subject motion and when image artifacts are present in acquired slices. In this work, we present NeSVoR, a resolution-agnostic slice-to-volume reconstruction method, which models the underlying volume as a continuous function of spatial coordinates with implicit neural representation. To improve robustness to subject motion and other image artifacts, we adopt a continuous and comprehensive slice acquisition model that takes into account rigid inter-slice motion, point spread function, and bias fields. NeSVoR also estimates pixel-wise and slice-wise variances of image noise and enables removal of outliers during reconstruction and visualization of uncertainty. Extensive experiments are performed on both simulated and in vivo data to evaluate the proposed method. Results show that NeSVoR achieves state-of-the-art reconstruction quality while providing two to ten-fold acceleration in reconstruction times over the state-of-the-art algorithms.