Cursor has mind of its own

[zaphod42]

I notice this most often in Excel, but often times it will happen when the only thing open is a game (Dune2000), or when I am just on the internet.
The effect is not usually immediately, it often starts up after I have been on the computer for awhile.
System resources are around 80%. I have done a Norton Virus system scan, and I have updated virus definitions.
I have also recently done an Adware Spyware sweep.

I have recently replaced my fans (two), one on the back of the computer, and one directly on the cpu.
The computer is a 99 Monorail, and the cpu is a celeron. 450mghz. Memory is down to about 850mb.

Help

 

[Muscles]

I've had this problem on one of my office computers and a home computer as well quite awhile ago. Both problems were solved by buying a nice new mouse. Never appeared again.

 

[zaphod42]

Oops I meant to add that I have tried several different mice on this bad boy.

 

[Schadenfroh]

backdoor trojan run housecall from trend antivirus

 

[mechBgon]

Along with that, do you have a hardware or software firewall, and is your computer fully patched-up? What OS do you have?