There is no such thing as anti virus, malware whatever software.
How it works is CA or whomever discovers a a new virus or whatever in the wild. They analyze it, see what it installs where and note it's signature.
They then add this information to the list of malware they already check for and send you an update.
You download and install the update and scan your system.
It's not an anti virus package rather an application to look for known types of "bad stuff".
And there in lies the problem. From when the virus is released into the Internet until you download and run a new update you are vulnerable.
You can be running the finest most expensive anti virus package available and you can still get all kinds of bad stuff.