Every virus is malware, but not every malware is a virus.
A virus is just one of the many variants of malware.
Others are (not limited to):
- Browser hijackers
- Ransomware
- Trojans
The naming anti-virus is basically a misnomer nowadays.
In, what you could call "the old days", the only malware where viruses and that is where the name of the tools originated from.
A better name would be anti-malware (or something like that).
Unfortunately it is not possible to create one tool that protects your system from all harmful things.
If you would take all people from the best av vendors and give them the fastest super-computer, they still won't be able to create such a tool.
Look at it like a disease for humans or animals.
Scientists (doctors) and such, can only start looking for a cure if the the disease is known. (how it works, what it exactly does etc).
As for "defense" against malware it is the same.
A defense strategy can only be developed if the way of attack is known.
As there is no tool that can detect/protect against everything it is a must to run multiple tools for the best protection.
I recommend to have at least McShield, Kasperky and Mbam.
Although they do overlap, each can detect things the other can't.
But security doesn't start with a tool, but with what the user knows and does !
I've seen system infected with over 20 different malware.
Guess why ?
There where security tools installed and they gave a warning.
But the user had no clue what they meant and/or what to do, so the user just clicked on continue and not on "fix".