Almost two million PCs globally, including machines inside UK and US government departments, have been taken over by malicious hackers.
Security experts Finjan traced the giant network of remotely-controlled PCs, called a botnet, back to a gang of cyber criminals in Ukraine.
Several PCs inside six UK government bodies were compromised by the botnet.
Finjan has contacted the Metropolitan Police with details of the government PCs and it is now investigating.
A spokesman for the Cabinet Office, which is charged with setting standards for the use of information technology across government, said it would not comment on specific attacks “for security reasons”.
“It is Government policy neither to confirm nor deny if an individual organisation has been the subject of an attack nor to speculate on the origins or success of such attacks.”
He added: “We constantly monitor new and existing risks and work to minimise their impact by alerting departments and giving them advice and guidance on dealing with the threat.”
Read the full story on the BBC News website.