Science paper piracy site Sci-Hub shares lots of retracted papers

"Researchers obtained a list of nearly 17,000 retracted papers and searched for them on Sci-Hub. They then visually examined the documents that were returned. They found that 85 percent of them contained no indication that the paper had been retracted. "The availability of [unlabeled retracted articles] in the field of health sciences is particularly high," they note, "which indicates a significant risk of their unintended use and further citation in future research." ..."