Yeah modern computers are nowhere near as vulnerable to magnetic fields they used to be. There remains a risk however that data passing along unscreened wires could be corrupted. There is a risk that you might damage data on a card with a magnetic strip on it if placed near a magnet. A weak magnet should be okay, but if you put a strong magnet, like a neodymium iron boron magnet (like you find in a speaker) near electronics you may induce an electric current which could cause problems and hardware failure. Magnets can also attract debris, e.g iron dust particles that could get onto pcbs and cause short circuits. It's just good practice to avoid magnets.