LONDON (AP) — The sophisticated cyberweapon which targeted an Iranian nuclear plant is older than previously believed, an anti-virus company said Tuesday, peeling back another layer of mystery on a series of attacks attributed by many to U.S. and Israeli intelligence.

The Stuxnet worm, aimed at the centrifuges in Iran’s Natanz plant, transformed the cybersecurity field because it was the first known computer attack specifically designed to cause physical damage. The precise origins of the worm remain unclear, but until now the earliest samples of Stuxnet had been dated to 2009, and The New York Times — in the fullest account of the attack published so far — traced the origins of the top-secret program back to 2006.