One of the most sophisticated pieces of malware ever detected was probably targeting "high value" infrastructure in Iran, experts have told the BBC.
Stuxnet's complexity suggests it could only have been written by a "nation state", some researchers have claimed.
It is believed to be the first-known worm designed to target real-world infrastructure such as power stations, water plants and industrial units.
It was first detected in June and has been intensely studied ever since.
"The fact that we see so many more infections in Iran than anywhere else in the world makes us think this threat was targeted at Iran and that there was something in Iran that was of very, very high value to whomever wrote it," Liam O'Murchu of security firm Symantec, who has tracked the worm since it was first detected, told BBC News.
Some have speculated that it could have been aimed at disrupting Iran's delayed Bushehr nuclear power plant or the uranium enrichment plant at Natanz.
However, the worm has also raised eyebrows because of the complexity of the code used and the fact that it bundled so many different techniques into one payload.
Security researchers are scratching their heads trying to determine the origin of the Stuxnet worm, a piece of malware that targets large industrial control systems. Judging by the way it's constructed, the information it targets and some of the organizations that have been hit, the worm may have been created by a national government. Others, however, have their doubts.