7.Media Files. Unauthorized media files are dangerous both because of their content and what can be hidden in them. Video and music files are an increasingly popular method of sneaking malware into an organization, including spyware, Trojans, viruses and just about any other kind of bad stuff you can think of.

One popular method is to include code in a media file that exploits security flaws in the media player. For example, the infected media file can open a malicious Web page on the user's computer and use that to automatically infect the system - and from there the network. Since these attacks require minimal interaction from the user, often he or she isn't even aware of what has happened.

Even the recording industry has got in on the game. In 2004, a company working for the record companies started seeding file-sharing sites with media files containing a Trojan that downloaded adware and opened multiple pop-up windows on the user's computer.

Even if the files don't contain hidden nasties, the files themselves can be problems, with copyright violations and pornography the most obvious example.

8.Unnecessary Modems. A lot of computers, especially older ones, included built-in modems whether or not they were needed. In other cases, servers have modems connected directly to outside lines for purposes of monitoring and maintenance. In either case, unneeded modems provide another path into your network, an unnecessary path that brings with it a host of potential problems.

War dialling isn't as popular an attack as it once was, but some bad guys still use it, and an unprotected modem attached to your network is just as dangerous as ever.