Welcome to the next round of open-source software patent litigation.  This time, it's antivirus software maker Trend Micro versus Barracuda Networks and ClamAV, and Barracuda isn't going down without a fight.

The short version: Antivirus software vendor Trend Micro filed U.S. patent 5,6230,600 back in 1995, which it claims covers antivirus scanning on a network gateway.  It has since brought suit against Barracuda Networks for using the open-source ClamAV product in its network-gateway protection devices.  According to Trend, ClamAV violates Trend's patent; either it needs to be removed from Barracuda's products or Barracuda needs to pony up a license fee.

Barracuda's stance: Trend's patent should be voided.  There are plenty of examples of prior art for this sort of thing, it claims; it cites seven examples right on its page about the whole issue.  That said, Trend has brought legal action against other companies -- not folks using open source software like this, though -- for also violating the patent.

What makes the case interesting is not only the fact that Barracuda is not lying down, but that quite a few other folks have stepped up to side with Barracuda.  Among them are some easily recognized open source luminaries, such as Eben Moglen and Richard Stallman, but there's also an as-yet-unnamed executive of another anti-spam company who's concealed his identity "to avoid being the next litigation target."

Barracuda's also on the hunt for a legacy product that it feels may bolster its case:

... we believe that a product called MIMESweeper 1.0 from a company called Clearswift, Authentium, or Integralis anticipates several claims of the '600 patent. We have yet to locate a copy of this product and would appreciate anyone who has a copy sending it our way.

Time to check your attic?