Extremely long scan time?

I recently updated to the CIS 5.3.17 and it takes 13 hours and 33 minutes for the antivirus program to scan my computer. Prior to that update, my computer was scanned in 45 - 60 minutes. The program settings and computer settings are all the same.
I currently run Windows XP SP3 on a Pentium 4 3.2GHZ processor, with 2 GB RAM, on a 500GB hard drive. The computer was fully reinstalled about a month ago.
I’ve tried some experiments on other computers, 1 running Vista and another running Win 7 (64 bit for both), and the scan time on 5.3.17 well exceeds the 60 minutes that the previous version used to take.
I contacted support, but their answer was to download ‘GeekBuddy’ to allow technicians onto my computer–which I’m uncomfortable with doing.
Has anyone any thoughts about this issue?
Thanks in advance
Keith

That sounds like there could be a compatibility problem with one of your applications.

Windows 7 and Vista come with a cool Resource Monitor tool. Just type in resource in the search field in the Start Menu to start it.

When it is running see if you can cross reference cpu and disk usage by cmdagent.exe to disk or cpu usage from other programs. In the past I have seen cmdagent.exe getting dragged along a bit by Trusted Installer process .