First, because antivirus programs are playing "catchup" against malware and vulnerabilities, they always seem to be a little behind.. And second, because "vulnerabilities" within the operating system are frequently not addressable by antivirus programs, it takes the user of the computer AND Microsoft to correctly patch the machine before the malware can be effectively blocked.
It brings to mind the serious problems my government employer had, years ago, with the Blaster worm.. Once Microsoft correctly patched the "hole" AND each department patched their computers, the worm became a non-issue. At the time, I was the IT person for our department, I stayed ahead of the game, and I had our computers patched BEFORE the Blaster worm was released. As a result, our department ran smoothly while others had temporary stoppage till their computers could be fixed.
Hope this helps.
Grif
BTW, I run Avast.
http://www.pcworld.com/article/261075/antivirus_suites_struggle_to_block_exploitbased_attacks.html#tk.rss_news

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