Renattach is a small, efficient and surprisingly effective filter designed primarily to offer an additional level of safety to Windows users whose e-mails pass through a UNIX-like mail server. Many modern viruses are spread through e-mail, and renattach combats such viruses by filtering e-mail attachments based on file extension. The idea is to rename potentially dangerous attachments (executable ones) so that the user, or the user's poorly written e-mail software, does not accidentally execute the attachment.