Well, you have obviously not been the victim of the latest Ransomware viruses that use Bitcoin as a payment option. Our company was targeted for this and all the computers with outdated AV Software got infected and files got encrypted. The other computers with the latest updates are still running without any problem.
A lot of viruses are doing things on your computer, without you even knowing it and it is only when you install a good AV software, that you realize what viruses are running in the background and once you look at the payload description for that viruses, a lot of the weird things that are happening on your computers becomes clear.
We had a bot network running on 100s of computers with outdated AV software and when we manually updated it, the bots was removed and the users reported back that the computers was much faster than before.
