Spyware and virus are great threat to computers. Stealthily and surreptitiously a spyware can find its way into your system.  You need good anti-spyware to stop and remove the intruder program.  You need to be careful when you make purchases online via credit card and have internet banking. 

When you download anti-spyware program from the internet, make sure that it is from a good company.  Otherwise after you install and run the program you may find that it fails to execute its duty.  You may realize belatedly that your new anti-spyware is actually a spyware in disguise. 

Furthermore, you may receive warning messages saying that you need to download more anti-spyware software from the malicious spyware site.  If you download more programs, you will, in fact, be downloading more viruses.  This could be one major reason for anti-spyware failure. 

So now you know what anti-spyware to download.  Reliable, genuine and effective program but after sometime you may find that it is unable to remove spyware.  Why is that so? The reason is spyware and viruses keep evolving day by day.  Newer and deadlier viruses are on the prowl.  So keep updating your anti-spyware every day.  Older versions will be incapable of battling against newer enemies. 

Thirdly the anti-spyware that you use can remove all types of spyware and virus.  Otherwise, some spyware may sneak in and you may not be able to remove it. 

The health of your computer is important.  Today we live a virtual life.  Our shopping, banking and education is all done online.  So follow safety precautions diligently.