I agree with John...it 'sounds' like a hardware problem...like a short or something....even one key sticking or getting 'loose' might trigger funny jumps. A malicious program would likely do more serious stuff.

There are issues about memory..(how much cache is being used..etc.)...or how much of the CPU is being used at the moment that might play a part.

I'd do tests with all non-essential programs closed, then try something like Mudcat for awhile and see if it still happens.

(It's ALWAYS hard to trap an intermittent problem!)