Even then, in some cases, this opting out does not always seem to work as intended.
Beware of rather then standard anti-virus definition (signature) detection software only.
The security community is in a constant state of change as new infections appear and it takes time for them to be reported, samples collected, analyzed, and tested by anti-virus vendors before they can add a new threat to database definitions.
Further, if you're dealing with it's unlikely the anti-virus is going to detect anything.
These kits come with pre-written exploit code and target users running insecure or outdated software applications on their computers.
and change them anytime you encounter a malware infection, especially if the computer was used for online banking, paying bills, has credit card information or other sensitive data on it.
You should and change all passwords immediately as a precaution in case an attacker was able to steal your information when the computer was infected.
This means using programs that can detect when malware is in the act of modifying/encrypting files AND stop it rather than just detecting the malicious file itself which in most cases is not immediately detected by anti-virus software.