Computer assistance required?

currently i'm using firefox and enjoy it more than explorer for various reasons, currently i do this after close out firefox.

clear browsing history

download history

saved form and search history

cache

cookies

saved passwords

authenticated sessions

i do fully understand .exe, i currenly run ad-aware and zone alarm to, at least in a way that helps maintain my pc to help avoid spyware and viruses, but my question is though, how much does it really help though, are there others way stuff could be implanted on my pc without my knowledge, i'm not talking about opening email from unknown users, or someone coming to my house and planting one, i know various websites can probably do without your knowledge, or websites that look like a similiar one but aren't, so how else can i found out besides downloading 4 or more antivirus software and spyware or using different format styles like a .xls / .doc, etc, any information would be useful

Computer assistance required?antivirus software

Sounds like you do what you should with Firefox and with a firewall and for spyware. However, you really should have an anti-virus program, too.

Common sense in using safe(r) surfing and email habits, a good firewall, a good anti-virus, and some decent spyware protection -- as long as you also download and install security patches and updates from Microsoft -- is about as good as you can get.