With quite a few anti virus software to pick, it is common to see users changing anti virus softwares.
When removing the old anti virus software to install a new one, Windows Add/Remove program doesn’t completely remove everything. Traces are still everywhere in your registry.
There are specific softwares written to remove a specific anti virus. Steve Yu have list down quite a handful of anti virus removal tool on his site MyTechQuest. Among the removal tools he has listed down are for the following anti virus softwares.