"Do you remember a couple of years ago Barracuda Networks asked us to help find prior art to help deal with a Trend Micro patent on, believe it or not, blocking viruses at the gateway, of all obvious things?
You did find some, the ITC then said the patent, #5,623,600, was invalid, and you'd think that would be the end of that.
But no, software patents live in their own illogical alternate universe, and because Trend Micro and Barracuda settled instead of getting a court ruling of invalidity, Trend Micro was free to threaten others and to continue to take in royalties on that patent. "
"Late in 2008, after the Barracuda revelations, Fortinet told Trend Micro it thought its patent was invalid and that it didn't think it should have to pay royalties on an invalid patent, and when Trend Micro didn't agree, Fortinet filed suit, seeking a declaratory judgment of patent invalidity not only regarding the '600 patent about gateways, but also on a '943 patent, "Apparatus and Method for Electronic Mail Virus Detection and Elimination", which Fortinet describes as "a continuation-in-part of the application that eventually became the '600 patent". Trend Micro got some claims tossed by saying the license agreement Fortinet signed precluded them, and it added a counterclaim for breach of contract."
Fortinet asked for help to find (more) prior art to invalidate the patent once and for all. More details on the nasty court battle, legal filings etc can be found at Groklaw.
Source: Groklaw http://www.groklaw.net/article.php?story=20100603011319457