A worker walks behind a logo at the IBM stand on the CeBIT computer fair in Hanover in this February 26, 2011 file photo. Warren Buffett said on November 14, 2011, his Berkshire Hathaway Inc has accumulated a 5.5 percent stake in IBM, the billionaire investor’s biggest bet in the technology field he has historically shunned. REUTERS/Tobias Schwarz/File (GERMANY – Tags: SCIENCE TECHNOLOGY BUSINESS)
