Spreadsheets are widely used in industry: it is estimated that end-user programmers outnumber programmers by a factor 5. However, spreadsheets are error-prone, numerous companies have lost money because of spreadsheet errors. One of the causes for spreadsheet problems is the prevalence of copy-pasting. In this paper, we study this cloning in spreadsheets. Based on existing text-based clone detection algorithms, we have developed an algorithm to detect data clones in spreadsheets: formulas whose values are copied as plain text in a different location. To evaluate the usefulness of the proposed approach, we conducted two evaluations. A quantitative evaluation in which we analyzed the EUSES corpus and a qualitative evaluation consisting of two case studies. The results of the evaluation clearly indicate that 1) data clones are common, 2) data clones pose threats to spreadsheet quality and 3) our approach supports users in finding and resolving data clones.