An anti-virus firm says the cyberweapon that targeted an Iranian nuclear plant is older than previously believed, a finding that may shed more light on a mysterious series of attacks attributed by security experts to U.S. and Israeli intelligence.

The Stuxnet worm, which experts believe damaged or destroyed centrifuges at Iran's Natanz plant in about 2009, revolutionized the cybersecurity field because it was the first known computer attack specifically tailored to cause real-world damage.

Previously the earliest samples of Stuxnet dated from 2009, but Symantec's findings push the timeline back.

The company said late Tuesday it found a primitive version of the worm dating back to November 2007 and that one element of the program dates to late 2005.

U.S. and Israeli officials have declined to comment on the attacks.