All programs below are FREE so there is really no excuse not to have some of them.
Anti-Virus
AVG Free Edition - Very good program for free. Not as good as Norton or Kaspersky but you should run SOMETHING.
Avast! - Same as above.
Panda's 38-in-1 Virus Removal Tool - This gets rid of quite a few of the more common viruses but only those 38. This is something good to run if you can't get online and is small enough to fit on a floppy.
Trend Micro PC-Cillian Online House Call - Online Virus Scan.
Panda Platinum 7 Anti-virus - Another good anti virus program that has 1 year of free updates.
eTrust EZ Armor Security Suite - Includes the eTrust AV program and eTrust Firewall (rebranded ZoneAlarm) which is one that a lot of corporations use and you get 1 year of free updates to the AV and the firewall. HIGHLY RECOMMENDED SOLUTION.
Trojan Removal
PC Flank Trojan Scan - Online scan of your system to see if you may have a Trojan.
TrojanScan.com - Online scan to see if you may be infected with a Trojan.
Trojan Hunter - Very good program with a 30-day free trial which is just fine if you think you have been infected with one.
TDS-3 - Same as above. 30-day free trial with some missing features.
Emisoft On Demand Trojan Scanner Another free on demand Trojan Scanner.
Firewalls
Zone Alarm - Very good firewall that is easy to use and will keep most stuff from getting in or getting out.
Sygate Personal Firewall Free - Good free and easy firewall like ZoneAlarm.
eTrust EZ Armor Security Suite - Includes the eTrust AV program and eTrust Firewall (rebranded ZoneAlarm) which is one that a lot of corporations use and you get 1 year of free updates to the AV and the firewall. HIGHLY RECOMMENDED SOLUTION if you don't already have a firewall and antivirus you are currently using.
Kerio Personal Firewall - Rules based firewall like Zone Alarm. More powerful as far as rule sets but not for the beginner.
Note: XP users please for the love of God at least turn on the included firewall. Please? It's better than nothing.
System Scans - See what is open on your computer and where you may be open to attack.
BroadbandReports Port Scan - See what ports are open on your computer.
PC Flank Stealth Test - Make sure your computer is unseen to the outside world.
PC Flank Browser Test - See if your browser reveals any of your personal information.
PC Flank Exploits Test - This test will detect how vulnerable your computer is to exploits attacks.
PC Flank Advanced Port Scanner - This test will scan your system for open ports that can be used in attacks on your computer.
GRC LeakTest Program - Good test to make sure your firewall is behaving as it should.
GRC ShieldsUP! - Another firewall scan to see what ports are opened or not.
Spyware/Adware Removing Tools
Spybot S&D - One of the most up-to-date removal tools you can get. You'll find a lot of crap on your computer
Ad-Aware - Good program. Not as good as Spybot but will pick up some stuff Spybot might miss. Same with Spybot picking up stuff Ad-Aware misses.
Spyware Blaster Another spyware removal tool. Free but I haven't tried it yet.
HijackTHIS - Removes browser hijacking (redirecting to other sites like Casino site when you are trying to go to Google.com etc).
Browsers
Mozilla 1.4 - Includes pop-up blocking in the browser itself.
Mozilla Firebird - Really cool. Has pop-up blocking AND tabbed browsing. Tabbed browsing owns.
Avant Browser - Addon to Internet Explorer and adds pop-up blocking and you can have multiple browser windows. Updated constantly.
Opera - Good browser and very fast. There is a free version with a ad banner so if it doesn't bother you then its a good choice as well.
E-mail Clients
Incredimail - Has cool features like backgrounds, handwritten sigs, etc.
Eudora - Alternate to Outlook and Outlook Express which most viruses are targeted at. Free version has small 3/4" add in the lower right but not really noticable. Paid version also includes SPAM filter.
Mozilla 1.4 - Includes pop-up blocking in the browser itself plus includes Communicator E-mail client that is very good.
SPAM Blockers
Mailwasher - Good program. I use this at home. You run it before you check e-mail with your e-mail client and it will automatically tag e-mail as SPAM (you can also add stuff to blacklist) and can bounce the e-mail back and also delete it before it hits your Inbox. The bouncing is good because it gives the appearance that your e-mail addy doesn't exist. Free version only checks one account. Note: This is for POP3 e-mail (ie. Hotmail, Yahoo mail is not available but the Paid version can check Hotmail.)
Shoot The Messenger - A small (only 22Kb, takes five seconds to download on a slow connection) and simple to use program that will stop Windows Messenger Service spam (gray boxes that appear in the middle of the screen.)
Pop Up Blocking
Google Toolbar - Add-on for Internet Explorer. Google Labs has some cool shit and the newest thing included in their Toolbar is pop up add blocking. Easy to use and install/uninstall.
Pop-Up Stopper Free Edition - I've heard this works fairly well but I have never used it personally.
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You should at least get one of the virus scanners and one of the firewalls I posted. You will do yourself a favor by being somewhat protected from viruses and worms like MSBlast and SoBig. I am amazed at how many people foolishly run their computers with no protection whatsoever and end up fucking over everyone else in the process.