The deeper I delve into Windows security holes, the more clueless Microsoft seems. An arcane feature in XP called Remote Assistance gives control of your PC to another user on a remote computer. Don't get me wrong; this feature is a useful tech tool. The problem is that it's woefully undocumented. And Microsoft enables it by default! It resides on the Remote tab in System Properties.
To disable Remote Assistance
Right-click My Computer.
Select Properties.
Click the Remote tab.
Uncheck Allow Remote Assistance Invitations to be Sent from This Computer.