dstiles - 7:15 pm on Aug 29, 2013 (gmt 0)
There are a LOT of "malicious" user-agents including those you mention. The specific discussion here refers to user-agents emanating from google and purporting to be valid google agents.
Mozilla/6.0 (compatible) is a generic UA used by (as far as I can determine) proxy servers such as bluecoat. They are harmless and require only a temporary block, not a full-blown IP ban.