How is Adobe's PDF Reader like a swiss cheese factory? If you don't need Adobe's bells and whistles, kill it with fire and download
Sumatra PDF or
Foxit's free reader instead.
Antivirus and Antispyware Programs
Two free antivirus/antimalware solutions dominate the competition at this point:
Microsoft Security Essentials is, in a twist of irony, now the better of available antimalware/antivirus products, replacing Windows Defender and Windows Live Onecare. It is free (in general) and quite effective. As of version 2 it works on all versions of Windows XP, as well as Vista and 7.
Antivir by Avira is the best of the free ones for personal use, using the retroactive tests by AV Comparitives as a guideline. Updates can frequently be painfully slow, but it's a solid product. It does nag you to purchase stuff, however.
If you are in the market to actually purchase something, I recommend going to
Antivirus Comparatives to compare them. Particularly, look at their retrospective and performance tests. You'll see MSE and Antivir do rather well, so focus on the ones that provide better results than them (obviously, if you're going to be paying for it). F-Secure and Eset are probably the two with the most solid reputation that you may not have heard of.
Malwarebyte's Anti-Malware - Currently the 'main' anti-malware program. You might need to rename the executable and run it from the command line from safe mode, meaning you need to download and run both the install program and database update from elsewhere onto eg a flash drive.
SUPERAntiSpyware - Another antispyware program that comes with good recommendations.
Hijackthis is useful to have other members analyze your system, if there is a need. It sometimes picks up on newer software that others miss.
Security and Privacy Utilities
Crap Cleaner err, CCleaner. I had forgotten about this one. Don't pay for registry cleaner programs.
Password Safe - Handy utility for managing hundreds of passwords for Windows.
KeePass Password Safe - Another Windows Password Keeping Utility
Advanced Security Programs
Just a place where I'm putting links for people with more technical experience. These should only be used by people very familiar with computers.
ComboFix -
LSPFix -
KillboxThe MVPS Hosts file - blocks ads and infested domains like mad. Since many sites use some of the sites this blocks for ad revenue, you may not want to use this, or at least be mindful of supporting communities, sites and software that you make heavy use of.