IT security firm McAfee claims to have uncovered one of the largest ever series of cyber attacks.
It lists 72 different organisations that were targeted over five years, including the International Olympic Committee, the UN and security firms.
McAfee will not say who it thinks is responsible, but there is speculation that China may be behind the attacks.
Beijing has always denied any state involvement in cyber-attacks, calling such accusations "groundless".
Speaking to BBC News, McAfee's chief European technology officer, Raj Samani, said the attacks were still going on.
"This is a whole different level to the Night Dragon attacks that occurred earlier this year. Those were attacks on a specific sector. This one is very, very broad."
Dubbed Operation Shady RAT - after the remote access tool that security experts and hackers use to remotely access computer networks - the five-year investigation examined information from a number of different organisations which thought they may have been hit. (more)