It starts with you!
Learn and practice safe surfing techniques.

First line of defense
A hardware type firewall.... This would be the built in firewall programs of routers even if a single computer user...put a router between you and the internet.

XP and Vista have software firewalls and are really mediocre to say the least
A top qualoty software firewall that is free is Comodo

Install a top quality anti virus program and keep it updated.
Install a top quality anti spyware/malware program and keep it updated.


Pretty simple!

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There will be some arguements over this:

There is very little differences in free and/or paid for versions of security programs....Paid for are mostly refered to as "suites" because they include an all in 1 package deal and support auto updating....the problem is that they are extremely intrusive and take over your computer.

Comparisions are based more on packages than one programs....thus the better all inclusive package the better the results in the comparision charts.

I have this installed on my computers. They are all free...

spywareblaster
spybot S&D ..............I also use Adaware personal on some other computers
Ccleaner
ATF cleaner
Avira anti-virus

I update and run them regularly