Activision Blizzard's ( ATVI ) stock price snowballed on Tuesday as the gaming giant re-released the original version of "World of Warcraft," marking the 15th anniversary of the classic game. ATVI shares shot up 4.7% to $51 as the Irvine, Calif., company's decision to re-release "World of Warcraft" free to subscribers also appeared to stoke enthusiasm among investors. Collister Johnson, president and chief operating officer, said in a statement that subscriber numbers starting ticking up in May after the company said it planned to re-release the classic version of World of Warcraft in August. "The `World of Warcraft' team is focused on delivering substantial incremental content in nonexpansion years," Johnson told analysts on a recent conference call, adding the company "will be supporting a release with a major awareness campaign."