F-Secure estimates there are over 300,000 viruses

Most AV vendors only highlight the most prominent new viruses, but they usually have to add dozens of new signatures daily to their detection files.  More amazingly, it's a miracle that AV software can even run, much less efficiently without impacting performance. 

AV vendors are always challenged by the growing signature file sizes, (e.g., McAfee's has almost doubled in the past 2 years).  There is alsooccasional need to adjust the scanning engine when new treats emerge in previously safe file types or system areas.  As one of friends recently stated, "AV Detection is Rocket science"   

F-Secure estimates there are over 300,000 viruses
http://www.f-secure.com/weblog/archives/archive-052007.html#00001198

QUOTE:  Question: How many viruses or malware exist in general? Can you give me some number? The approximate count is now over 300,000.