AMaViS (A Mail Virus Scanner) scans e-mail attachments for viruses using third-party virus scanners available for UNIX environments. It resides on a UNIX (Linux) machine and looks through the attached files arriving via e-mail, generates reports when a virus is found and sets the delivery on hold.
Email Security through Procmail (the Procmail Sanitizer) provides methods to sanitize email, removing obvious exploit attempts and disabling the channels through which exploits are delivered. Facilities for detecting and blocking Trojan Horse exploits and worms are also provided.
John the Ripper is a fast password cracker, currently available for many flavors of Unix, Windows, DOS, BeOS, and OpenVMS. Its primary purpose is to detect weak Unix passwords. It supports several crypt(3) password hash types commonly found on Unix systems, as well as Windows LM hashes. On top of this, lots of other hashes and ciphers are added in the community-enhanced version (-jumbo), and some are added in John the Ripper Pro.
MIMEDefang is a flexible MIME email scanner designed to do all kinds of email processing, including anti-virus scanning, anti-spam scanning, replacing parts of messages with URLs, adding boilerplate disclaimers, and so on. It can alter or delete various parts of a MIME message according to a Perl-based policy filter. It can also bounce messages with unacceptable attachments and modify SMTP response codes on the fly. It works with the Sendmail 8.11 and newer "Milter" API, which makes it more flexible and efficient than procmail-based approaches.
Qmail-Scanner, (also known as scan4virus) is an addon that enables a Qmail Email server to scan all gatewayed Email for certain characteristics. It is typically used for its anti-virus protection functions, in which case it is used in conjunction with commercial virus scanners. but also enables a site to react to Email (at a server/site level) that contains specific strings in particular headers, or particular attachment filenames or types (e.g. *.VBS attachments). It also can be used as an archiving tool for auditing or backup purposes. Qmail-Scanner is integrated into the mail server at a lower level than some other Unix-based virus scanners, resulting in better performance. It is capable of scanning not only locally sent/received Email, but also Email that crosses the server in a relay capacity. It also has SpamAssassin support.
renattach is a stream filter that can identify and act upon potentially dangerous e-mail attachments. It's a highly effective way of protecting users from harmful mail content (virii and worms) by disabling or removing attachments that may be accidentally executed by the user. It is written in pure C and can quickly process mail with little overhead. Unlike a conventional virus scanner, there are no specific virus or worm definitions. Instead, it identifies potentially dangerous attachments based on filename extension and on encoded body content. It can be used from within sendmail, postfix, procmail, or pretty much anywhere else.
RIG (Random Identity Generator) is a free replacement for a shareware program out there called 'fake'. It generates random, yet real-looking, personal data. It is useful if you need to feed a name to a Web site, BBS, or real person, and are too lazy to think of one yourself. Also, if the Web site/BBS/person you are giving the information to tries to crosscheck the city, state, zip, or area code, it will check out.