The Antivirus industry has a dirty little secret that they really don’t want anyone to know. Despite the claims of their marketing departments, their products are not all that effective in the real world. Many of them only protecting (at best) 80% or 90% against threats out there in the wild at any time, and their protection against ransomware is very bad.
Let us explain why. Antivirus products must protect against two general types of threats to be effective: known threatsand unknown threats. Known threats have a signature so good AV products should be able to detect the threat and get rid of it. That is what's known as reactive detection.
There will always be other unknown threats no matter how much protection there may be against known threats. As quickly as fixes are made, the bad guys are creating fresh new malware. AV products need to protect against new threats in a proactive way, therefore antivirus software can be scored by looking at how many new threats they are able to prevent.