In it’s ‘out-of-the-box’ condition, MS Windows is plagued with security problems and bad configurations that most users are unaware of, and securing that system from Internet predation & assault is not a single application, or a suite: and it’s not a "1 click does every fix" that so many want…it ain’t going to happen people.

It’s layers of protection, user habits, system configuration, real time protection; and most important, threat matrix awareness (because the internet is so fluid and dynamic, it changes almost hourly).
(Check for fairly current threats here: http://blogs.pcmag.com/securitywatch/top...

"Do-it-all" suites (CareOne, McAfee, or Norton, etc.) give users ‘feel good’ security, and lull them into complacency, which often has very bad results.

Core defense applications might include (but not limited to):
Avast! (anti-virus); http://www.avast.com/eng/home-registration.php
or Microsoft’s "Essentials" home version (freeware; 3 versions):
http://www.brothersoft.com/microsoft-security-essentials-251793.html

Kerio/Sunbelt Personal Firewall (free) is good entry level protection; paid version is excellent; http://www.filehippo.com/download_sunbelt_personal_firewall/
SpywareBlaster (snoopware prevention); http://www.javacoolsoftware.com/spywareblaster.html
>>>The #1 defense against any malware: Use a "Limited User" account & Firefox, with ‘NoScript’ add-on, with "locked down" settings<<< and dual browser set up as I describe here:
http://answers.yahoo.com/question/index;...
"Sandboxie": http://www.sandboxie.com/
for even better protection (not for 64 bit).
The key element or common principal is to keep rubbish from all sources out of your system in the first place: stopped @ your doorstep, with a layered defense.

Most novice users do not like hearing this, but nonetheless, it’s true: using Windows requires you to become a security expert, it’s that simple. Something they conveniently omit telling you when you buy this system…

If you don’t have time or desire to do all this, plus ‘updating’ everything, have a look @ "Secunia": checks all your 3rd party & OS updates, plus gives your system a rating (in %) of defense readiness…pretty handy.
Freeware.
http://secunia.com/vulnerability_scanning/

Mainly it is common sense, I use Avira (link below) and that covers me pretty well overall, also when browsing the internet I use firefox and an add-on called WOT, Web of Trust, which warns you about risky websites that try to scam visitors, deliver malware or send spam. Using those two things I haven’t had any problems for years

That usually comes down on your preference. You cannot be 100% safe from virus because as we all know thousands of viruses are made each day. That’s why a daily or couple of updates a day of virus database for an anti-virus program is performed for maximum protection. Some new, very good viruses do get passed some anti-virus softwares. So everyday you’re only 99.9% safe, 1% is a slim chance but still a possibility of infection.