Anti-Virus
Overall people are doing a good job at this. A couple of years ago, every second computer coming into a shop were filled with viruses. Get good quality anti-virus software, stay away from free stuff.
Spyware
"Spyware is programming that is put in someone's computer to secretly gather information about the user and relay it to advertisers or other interested parties." As such, spyware is cause for public concern about privacy on the Internet. Use a good quality spyware remover or get a shop to remove them for you. DO NOT respond to “pop-ups saying you have spyware, would you like it removed?”
Cool your computer
Heat will shorten the life of a computer. The motherboard will cook its capacitors. Do not park it up against a desk so it can’t circulate its air. Cat hair and dust will clog the vents. Blow it out yourself or ask someone who knows how to do it
Firewall
You have anti-virus, you have anti-spyware, but the enemy can still get in. Hackers can “ping” you address and “share” your hard drive
Upgrades and Memory
There are only 2 types of valid upgrades: more memory or a full motherboard/processor replacement. With a few exceptions, computers will always benefit from more memory. When you do a full motherboard/processor replacement you need to match up a processor, motherboard, memory and power supply and then install these components into your system. Everything matches and everything runs smoothly.
