A worker is pictured behind a logo at the IBM stand on the CeBIT computer fair in Hanover February 26, 2011. The world's largest IT fair CeBIT opens its doors on March 1 and runs through March 5. REUTERS/Tobias SchwarzReuters – IBM has agreed to buy British security analytics software firm i2 for an undisclosed sum, it said Wednesday, as it continues to devour companies that can help its clients deal with growing mountains of data.