安全软件如何防止未经授权从系统中删除？

It's been my experience that some security software (like Symantec's Norton AntiVirus) oftentimes prohibit their removal from a Windows system via the "Add or Remove Programs" utility, going so far as to occasionally require a removal program obtained from Symantec's homepage. (I assume this it to prevent a malicious program from disabling the security software... any other reason?)It's been my experience that some security soft