I started with this 12-year-old laptop that daughter.2 had used at university. Two of the keytops are missing, so I plugged in a USB keyboard and I hate trackpads so I plugged in a mouse. Then I installed Fedora Linux version 9 (which I used because it needs less memory than more recent versions). But when I tried to update it (yum upgrade) it didn't upgrade Firefox, which meant I couldn't install Adblock. I thought of messing around with it to try to get it to work, then I decided not to.
This means that now I have an up-to-date, fairly secure computer, which I'll only use for buying stuff (which mostly means Ebay, Amazon and Deal Extreme) and not for general surfing the web or email, so it's even less likely to get malwared than my usual Linux box.
It's quite surprising that a 12 year old laptop can still be useful! Thanks, daughter.2