Trend Micro acquired Identum in February 2008 for an undisclosed sum. Identum, which was founded in and later spun-off from the University of Bristol cryptography department, developed ID-based email encryption software. Identum's chairman was serial entrepreneur, Steve Purdham. The two companies were originally in talks for Trend Micro to license Identum's technology, but Trend Micro later decided to purchase the firm outright. Identum was renamed Trend Micro (Bristol) and its encryption technology was integrated into existing Trend Micro products. Existing Identum products were continued but sold under the Trend Micro brand. Also that year, Trend Micro sued Barracuda Networks for the latter's distribution of ClamAV as part of a security package. Trend Micro claimed that Barracuda's use of ClamAV infringed on a software patent owned by Trend Micro for filtering viruses on an Internet gateway. On 19 May 2011, the U.S. Patent and Trademark Office issued a Final Rejection in the reexamination of Trend Micro's U.S. patent 5,623,600.