i swear they do it deliberately
Last week I was certain my creaky old desktop computer (which is only 4 years old, but that's about 80 in computer-years) was dying. I kept locking up and shutting down suddenly for no apparent reason. It was taking me about an hour to even get it to boot up, and it kept giving me error messages about corrupted system files - but a different file each time.
I'm coming to the end of my OU course and I absolutely need a computer that works for the next couple of weeks, so at the weekend I went and bought myself a shiny new laptop, a printer, and an external hard-drive. I played about and got everything transferred during Sunday & Monday, and during that process I retrofitted the antivirus that came with the new laptop onto the old desktop as well.
Bloody thing hasn't given me a minute's trouble since.