Trend Micro
On January 29, 2008, Barracuda Networks was sued by Trend Micro over their use of the open source anti-virus software Clam AntiVirus, which Trend Micro claimed to be in violation of their patent on 'anti-virus detection on an SMTP or FTP gateway'. In addition to providing samples of prior art in an effort to render Trend Micro's patent invalid, in July 2008 Barracuda launched a countersuit against Trend Micro claiming Trend Micro violated several antivirus patents Barracuda Networks had acquired from IBM.