As the spywares are distinctively different from the computer viruses, they are not detected by anti virus software. Therefore, you can not know the existence of spywares in your PC unless you are having a
Microsoft anti spyware installed in your PC. It is not that only Windows operating systems are vulnerable to spywares. But as Windows is the most used operating system all over the world, the authors of the spywares find it more effective to create and spread spywares that are compatible with Windows operating systems. So if you are using a Windows operating system, it is always recommended that you regularly scan your PC with
anti spyware program to be safe from the ill effects of spywares.