It did not know what data the hackers had accessed but speculated that it was looking for information about the crisis in Ukraine.
A spokesman said that the company would roll out an automatic update to affected versions of Windows.
Other victims include energy, telecommunications and defence firms, delegates of the GlobSec conference about national security and an academic who was an expert in Russian-Ukraine relations.
"The malware has been around for years - it used to be a denial-of-service bot called Black Energy which these hackers have repurposed for their needs."
"The interesting thing is that when it is detected by IT staff it will show up as Black Energy, which they will see as a very old run-of-the-mill bug that didn't do much."
"Although we have also seen as many attacks from the Quedagh bug in Poland as in Ukraine and we can't really explain that," he said.