Read
here, it seems to be a conflict between PC Chillin and SpyBot. Get rid of one or the other....
PcScnSrv.exe: Performance Problems
Trend Micro Internet Security Suite 2007 (which many refer to as PC-cillin 2007) appears to be causing performance problems for many. This is particularly perplexing as previous versions of Trend Micro PC-cillin, notably the 2006 and 2005 versions, were applauded for their streamlined performance. The culprit in the 2007 version appears to lie in 'PcScnSrv.exe', a component of the suite that many claim is consuming 97% to 100% of cpu utilization and anywhere from 50-70 Mb of RAM. The result: programs are hanging, websites timeout, and the system runs so slowly it's difficult to even shutdown.
The solution: uninstall the 2007 version, reboot the system and then reinstall the 2006 version using the license key from the *2007* version. This will get you another year of updates and buy some time until Trend Micro resolves the performance issues. Rumor has it, a patch is in the works for sometime in January.
UPDATE: According to Trend Micro, the performance issue is a result of a conflict with the Immunize feature in SpyBot Search and Destroy. For details, see: PC-cillin Slowdown Traced to SpyBot S&D