I've been happily using the commercial virus scanner, Kaspersky for a few years now and have been very pleased with it.

However last year the 2010 edition was released and it introduced a problem with its rootkits scanner. This is an automated scan which it performs about 30 minutes after you boot your system, and again at scheduled intervals. However, the developers provided no way of changing how this works or disabling it.

The problem is that on many systems the rootkits scan goes wrong and can take hours to complete, rather than the minutes it is meant to, and it can grind a system to a halt whilst it completes this. I was getting this very behaviour, with the rootkits scanner running (shown by the Kaspersky K icon in the task bar pulsing) and when it hit 99% complete it would just remain stuck there and at this point all network access would become blocked and you could not access the internet or LAN at all unless you waited for the scan to eventually complete, or you reset and rebooted.

Thankfully users discovered you can switch this rootkit scanning off. It is a hidden feature so initially they edited the registry to do this. However, it is now much easier. The software supports custom skinning, and someone called Pipkin has released a new custom skin called Friday 3 skin, which adds a setting to switch rootkits scanning off, and also adds a lot of other additional features and settings missing from the default install.

Look at http://forum.kasperskyclub.com/index.php?showtopic=5895 for screenshots of the new skin and it's download.

This is worth it for any users of Kaspersky, even if you are not having this issue.