It sounds like "neglect"....When was the last time a tech or administrator checked ALL of the computers? Unfortunately, most companies don't do a lot of "maintenance" on their computers. I'm not sure how large your company is, but it takes a lot of time to keep the Windows patches current, plus run Scandisk/Chkdsk and Defrag on a routing basis. BUT someone needs to do it. The welfare of each computer will also depend on how often each user visits the internet. I work for an agency of some 8-10,000 computers of which I oversee about 30 or so. Like your's, almost all of them use McAfee as a antivirus solution, but there is a lot more going on behind the scenes. The agency uses McAfee's "ePO" program which allows for remote administrative computers to automatically install programs and update all computers on its' network. It also uses "gateway" software which prevents certain types of intrusion attempts, plus our Exchange mail server checks incoming mail and spam. In addition, I monitor and maintain all those computers that I am responsible for, just to make sure that all users and their computers are working well.
In your case, there are a number of things to do including making sure each computer is cleaned up regularly and depending on the operating system, Scandisk/Chkdsk and Disk Defragmenter are run on a regular basis. Make sure that all the current service packs and Windows Updates are applied as necessary. As "Roddy" mentioned above, you also need to check for spyware on each computer.
Hope this helps.