The spyware, called Regin, has been around for about six years and is clever enough to steal your passwords, go onto your hard drive and resurrect deleted files, and take screenshots.
Apparently, according to a Symantec executive interviewed on the BBC 4 radio programme Today, it has hit PCs in Saudi Arabia, Ireland and Russia.
But she declined to say which Western organisation had invented Regin and let it loose on the online world.
Symantec thinks the malware has parallels with the Stuxnet worm, jointly developed by cyber warriors in Israel and the USA to mess up Iran’s nuclear programme.
AV companies are now hustling to get an antidote out against Regin.