The new variant was designed for a different kind of attack against centrifuges used in Iran’s uranium enrichment program than later versions that were released, according to Symantec, the U.S-based computer security firm that reverse-engineered Stuxnet in 2010 and also found the latest variant.

The new variant appears to have been released in 2007, two years earlier than other variants of the code were released, indicating that Stuxnet was active much earlier than previously known. A command-and-control server used with the malware was registered even earlier than this, on Nov. 3, 2005.

Like three later versions of Stuxnet that were released in the wild in 2009 and 2010, this one was designed to attack Siemens PLCs used in Iran’s uranium enrichment program in Natanz.