Magnets need to be very strong or changing very quickly to affect electronics. They were a big concern with floppy disks and messed with CRTs but beyond that no magnet you're likely to come across is going to cause any effect on a PC (there are even strong ones in a lot of laptops). Even hard drives (the one common remaining magnetic component in systems) are unlikely to be affected.

Is a very good hypothesis... hum

But, wouldn't be those magnets too small for create a strong current? The computer should be protected from common sources of interference, right?