Ok I have Windows Defender. Along with SpyCatcher, AVG anti virus and AVG anti spyware, Spyware Terminator, VundoFix, Ad-Aware SE, Spyware Doctor and Spybot S&D. Reciently found that I have a pop up generator. So I did a scan with Windows Defenter can came back clean. I then did a scan with every single other program I have and EVERY program came back with multiple fairly serious threats. So basically 50 viruses got past Windows Defender. So obviously it does not find viruses effectively. Do what does it do? Should I just remove it?

Windows Defender is an anti-spyware tool not an anti-virus. Using more than one anti-spyware program increases your protection coverage. No single product is 100% foolproof and can detect and remove all threats at any given time. The security industry is in a constant state of change with new infections coming out on a daily basis. Each vendor has its own definition of what constitutes spyware and scanning your computer using different criteria will yield different results. The fact that each program has its own definition files means that some malware may be picked up by one that could be missed by another. Thus, a layered defense using several products to supplement your anti-virus and scanning in safe mode provides the most complete protection.