The Malicious Software Removal Tool is updated by Microsoft once each month, so that should tell you that the software removal tool is meant as a stop-gap rather than a primary line of defense. The Malicious Software Removal Tool isn’t a real-time anti-virus or anti-malware tool, though it will remove selected virus and malware infections. Unfortunately for some users, the Malicious Software Removal Tool is the only defense they use. Monthly updates are relatively infrequent for anti-virus and anti-malware packages, and sometimes, anti-virus removal/protection requires immediate action.
Should you rely on MSRT? It’s probably not a bad idea to run the tool. If you have no other A/V software, then running the MSRT is probably a given in your situation. (Something is always better than nothing when it comes to anti-virus software.)
Malicious Software Removal Tool does have the advantage of being free, and the updates are fee as well. Most other anti-virus software packages require you to license the base product and then pay for periodic updates for virus definitions. The virus definitions are what determine how effective (and up-to-date) your anti-virus protection is, so it’s not sufficient to license the base product and move on. The MSRT also runs in the background and will inform you of new infections it knows about.
Removing viruses isn’t part of Microsoft’s core business, however the company at least acknowledges that keeping up with the ever-growing amount of malware is tedious and time-consuming, and may tempt users to look at less lucrative targets like Apple or Linux as an option. With a regular (read: predictable) update schedule, however, I’d be somewhat concerned that malware producers may try to “time” their releases to maximize the amount of time between their malware release and the release of updated Malicious Software Removal Tool definitions in an effort to extend the run of new malware.
With the prevalence of malware “in the wild” having Malicious Software Removal Tool operational (it works for Windows 7, Windows Vista, Windows XP, Windows Server 2008, Windows Server 2003 and Windows 2000) on your computer is better than having defunct anti-virus protection or worse, nothing at all.