Best Free Adware/Spyware/Scumware Remover

A couple of years ago most folks relied on "SpyBot Search and Destroy" and "Ad-Aware" for spyware protection. Alas, spyware has evolved so quickly that these once outstanding products are no longer up to the task of providing primary protection, although they remain useful as secondary on-demand scanners.
The new generation of malware requires a new generation of products which provide stronger active protection and broader spectrum detection. The best anti-spyware programs (WebRoot SpySweeper, Spyware Doctor and CounterSpy) are all commercial products, but there are three free products that we can recommend that provide real time protection.
The first is a special cut-down version of Spyware Doctor that's available as part of Google Pack, which is a bundle of free software offered by Google. Called "Spyware Doctor Starter Edition”, the cut-down version lacks the full array of real-time-protection monitors possessed by its commercial big brother, but it still offers some active protection along with full scan-and-remove capabilities, scheduled scans, and free signature file updates. And on the subject of signature files, it should be noted that the signature files in Spyware Doctor Starter Edition are neither as large nor as up-to-date as those in its commercial big brother.
Your second choice is Microsoft's Windows Defender. Defender is the latest reincarnation of the excellent Giant Anti-Spyware product that Microsoft purchased late in 2004. Based on my tests, Windows Defender is not as effective as its immediate predecessor, but it still has solid protective capability. I tested it on several drive-by download sites. Its multiple real-time monitors provided a reasonable (though by no means watertight) defense. It appears to be a little vulnerable to polymorphic malware in particular, and for this reason we suggest it should be used in combination with regular on-demand scans from the free AVG Anti-Spyware. Our other reservation about Windows Defender is that it consumes quite a lot of your processing power. If you have a modern PC this should not be a problem. However, older machines will definitely suffer a performance hit.
A third choice is Spyware Terminator. Unlike Spyware Doctor or Windows Defender, it works with all versions of Windows, so it's the stand-out choice for Windows 9x users. It's no slouch either. Like Windows Defender, it has strong active protection. Indeed, with it’s built in HIPS system that warns you of any unrecognized intruders, it has stronger protection against unknown threats than the Microsoft product. This was confirmed on some tests I ran on drive-by download sites where Spyware Terminator proved to be impregnable.
Spyware Terminator has its own spyware detection engine, and gives you the option of using a second engine based on the Open Source ClamWin anti-virus program. ClamAV is not the most effective AV scanner on the market, but it's certainly competent and the additional protection can only be a plus. On the downside, Spyware Terminator is slow to scan and can slow down your PC a tad, though not nearly as much as Windows Defender. We've also heard reports that support via their free forum is poor.
Choosing between Spyware Doctor Starter Edition, Windows Defender, and Spyware Terminator is not easy. The full commercial version of Spyware Doctor has outstanding detection, but the reduced signature file size and weak active protection in the free starter edition is a concern. Defender is heavy on resources but has reasonable active protection. Its detection, however, is mediocre.
As of today, we think that Spyware Terminator has the edge as the best balanced product of the three, but it's difficult to see how free products like this can remain viable, particularly in a high support product class such as anti-spyware.
However, if you use an anti-virus product with good, active protection, such as the free version of AntiVir, you may well be tempted to go with Spyware Doctor. It's a product which offers reasonably good detection and excellent removal capabilities, and it's backed by regular and reliable signature file updates. Note: Spyware Doctor Starter Edition can be obtained via the Google Pack, but you can get it as a stand-alone download.
If all you're looking for is a tool to scan for and remove spyware/adware, then you should definitely consider SUPERantispyware. Even though the free version provides only on-demand scans, it has a growing reputation as the one to use for detection and removal of hard-to-kill strains. It's also one of the few new products to be added to the well known Spywarewarrior trustworthy antispyware list.
Another product in the same mould (the free version provides only on-demand scanning) is Malwarebytes' Anti-Malware. Although it's very new, it has a fine reputation because the organization behind it is well known for being a strong supporter of the fight against spyware, and has in the past released other excellent freeware tools like RogueRemover Free.
Threatfire is a respected and efficient active scanner for malware, and can considerably enhance the effectiveness of protection tools already installed. However, you should approach Threatfire with caution. My own experience is that the active scanner can be too aggressive and may block legitimate programs (or in some cases, components) installing. I particularly found this to be the case with ATI graphics drivers, where Threatfire refused to allow the Catalyst Control Centre to install. I encountered similar random problems with other program installations, although the majority of mainstream software did not suffer. If you need the enhanced and aggressive protection level that I've described, then Threatfire is a good option.
Finally, there is a simple option that very few people are aware of already built into Windows. I can only vouch for this in XP (and presumably Vista), though it may exist in earlier versions. Go to the start button and choose "Run". Once there, type "MRT" (without the quotes) and press enter. This will load Windows built in Malicious Software Removal Tool. It isn't even close to dedicated malware removal tools, but since it's a part of the OS already, it certainly qualifies as free software.