This is an insanely clever idea — basically, a website sells corrupted files; when you have to submit a paper via e-mail, you submit the corrupted file. It takes the professor a day or two to notice the problem, at which point he asks you to resubmit. You’ve just extended your deadline.

All profs have to do to stop it, however, is to require that in addition to an attachment, students paste the text of their papers into the submission e-mails. Or, profs could open the attachments right away to make sure they’re okay, and immediately request re-submissions.