A security company has unearthed some spying software dubbed miniFlame - which analysts believe may have been created by the US government.
The virus, which was discovered by Moscow-based Kaspersky Lab, has been carrying out precise attacks on targets in the Middle East.
Kaspersky said miniFlame had struck only 50 or so "high-value" machines, while Flame, a related program it unearthed earlier, had struck 5,000 computers.
Iran had previously blamed Flame for causing data loss on computers in the country's main oil export terminal and oil ministry.
"Flame acts as a long sword for broad swipes, while miniFlame acts as a scalpel for a focused surgical dissection," said Kaspersky researcher Roel Schouwenberg.
Not much is known about miniFlame's victims, with infections being found mainly in Lebanon and Iran, but also in the West Bank, Gaza, Kuwait and Qatar.
Kaspersky and US security software company Symantec said Flame's control software remotely directed a number of smaller programs - with miniFlame now identified as being among them.
Symantec said at the time the overall project "fits the profile of military and intelligence operations".
According to Kaspersky, miniFlame includes a "back door" allowing for remote control, data theft and the ability to take screenshots as the user engages with Microsoft Office, Adobe Reader, web browsers and other applications.
"MiniFlame is installed in order to conduct more in-depth surveillance and cyber-espionage," said Kaspersky chief security expert Alexander Gostev.
Kaspersky said it had found six versions of miniFlame, the most recent created in September 2011, but some of the protocols it used dated back to 2007, making it a long-running effort.
MiniFlame responds to a series of commands which were given the first-name codewords Fiona, Sonia, Eve, Elvis, Drake, Charles, Sam, Alex, Barbara and Tiffany.
The Elvis command, for example, creates a process on an infected machine, Barbara takes a screenshot and Tiffany directs the computer to a new command server.
US defence secretary Leon Panetta recently warned Washington could launch a pre-emptive strike against foreign cyber attacks that could cause "significant physical damage" or kill US citizens.
He said Washington was rewriting its rules for engagement in cyberspace, although the Pentagon has said little in public about what it can do.