1. On UNIX, a user can place an e-mail address in his ".forward" file. This will cause all e-mail sent to his account to be forwarded to that e-mail address. This file a is prime target of attackers. If they can overwrite this file, they can subtly start capturing the user's e-mail. This is especially dangerous if the the account in question is the root account. Note that the user doesn't have to know any about this file or have one on his system. The mere creation of this file by the intruder will activate this feature. Furthermore, since this file starts with a 'dot', it is normally hidden from the user, so they won't even be ware that this feature exists. From Hacking-Lexicon