Email and peer-to-peer networks also rank as significant venues for malware attacks, which have increased slightly in the U.S. but declined in Europe, according to Panda Security.

The motivation behind the $7.68 billion deal is unclear, but Intel says it wants to integrate computer security into its hardware.

First reported in December 2009, the bug has been fixed on all major browsers but Microsoft's.

The malware spreads through removable drives even if AutoPlay is disabled, installs rootkit on the computer.