The average computer user is aware of anti-virus and anti-spyware programs, but do they really work at removing your infection? In my experience, they do not work, at least not 100% of the time or even close to that.
If you ask any experienced and competent IT professional what to do about an infected system, they should only give you one answer: format your hard drive and reinstall your operating system. Why skip straight to the format / reinstall and disregard the anti-virus and anti-spyware removal tools?
1. Formatting and reinstalling your operating is the only 100% guaranteed way of removing an infection. Formatting your hard drive will, for all intents and purposes, remove all data from your hard drive, including any malicious code. Anti-virus and anti-spyware applications can almost never find and remediate every single infection (that is why you may have heard to use multiple anti-spyware scanning tools).
2. Virus and spyware removal can take many, many hours to complete. First you have to scan your computer, then you must remove the infections. If you're using multiple anti-spyware applications, you will have to scan and restart with each piece of software. The usual run time is about 1-2 hours depending on the speed of your computer and the size of your hard drive. Add in multiple scans and you can easily see how this can take up lots of time.
3. Formatting your hard drive and reinstalling your OS does not take as much time as you think it would. An average format / reinstall should be about 2 hours on the high end. This is probably less time than it would take you to run your anti-virus and anti-spyware programs.
4. In my experience, use of spyware and virus removal tools can lead to no results, unexpected results, or even a completely unusable computer. Say you have an infection on your computer and you run an anti-spyware application. The program may not completely remove the infection, leaving it to populate on the next reboot. Even worse, the scan can trigger some malicious code and leave the computer completely unusable (eg locks up at the log on screen, wipes entire hard drive and partition tables). Because of these headaches and uncertainty, it is best to just skip ahead and do a format / reinstall.
5. Computer security is proactive, not reactive. The point of anti-spyware and anti-virus programs is to keep malicious software off of your computer, not to remove the infection once it starts. It is much easier to identify malicious software and keep it off of your computer than it is to remove the infection. Everyone's computer is different and there is no way to accurately provide remediation options for every single piece of malicious software. Look at it in terms of probabilities. While there may be a 50/50 chance that your anti-spyware / anti-virus program will remove the infection, there's a definite 100% chance of removing the infection by formatting your hard drive and reinstalling your operating system.
To sum it up, there is no guarantee that anti-spyware and anti-virus programs will remove an infection. The only guaranteed infection removal method is to format your hard drive and reinstall your operating system. Formatting your hard drive will remove all data from your hard drive, including any malicious software you may have acquainted. On top of that, a format and reinstall typically takes less time, and can save you the headache of running a full fledged scan with multiple pieces of software.