Sadly, you will need more than one, not all of them will detect everything so here is the list I suggest:
1 – Microsoft Security Essentials; this one is the lamest but provides real-time protection, maybe Microsoft will assign a team of real developers to this one day; I truly think that this was done by a team of interns as a summer project
Download it here: http://www.microsoft.com/security_essentials/
2 – SUPERAntiSpyware, this one is the real deal, it detects and removes Spyware, Adware and Remove Malware, Trojans, Dialers, Worms, KeyLoggers, HiJackers, Parasites, Rootkits, Rogue Security Products and many other types of threats, not the easy ones but also the hard ones, the ones that Security Essentials, Norton and McAfee can’t detect!
The paid version provides real-time protection and it’s only $9.99, I think it’s worth it.
Download it here: http://www.superantispyware.com/
3 – Malwarebytes, this one is also a great one.
Download it here: http://www.malwarebytes.org/
And yes, you need them all, make sure to update them right before every scan and you know what? I think you should install #2 and #3 now, update them then boot into Safe Mode and run a full system scan, I promise that you will be surprised!
Hamid Alipour is a partner in Codehead, LLP with his wife, Tess. Hamid speaks 12 markup and programming languages [Yes, 12: PHP, CSS, Ajax, JavaScript, HTML/XHTML, Java, Python, C/C++, ASP, Visual Basic, Scheme and Action Script]; has a penchant for solving the unsolvable; an affinity for clean, hand-written code and is a Zend Certified 