The European Commission, including the body's diplomatic arm, has been hit by what officials said on Thursday was a serious cyberattack.
The attack was first detected on Tuesday and Commission sources have said that it was sustained and targeted.
External access to the Commission's email and intranet has been suspended and staff have been told to change their passwords in order to prevent the "disclosure of unauthorised information," according to an internal memo to staff. Staff at the Commission, the European Union's executive and regulatory body, have also been told to send sensitive information via secure email.
The event came just days ahead of the European Council summit being held on Thursday and Friday. The summit brings together the leaders of EU member states and crucial decisions will be made on economic strategy, the war in Libya and the future structure of the EU.
This led to early speculation that the source of the attacks may be Libya, but the Commission was quick to rule this out. The attack is thought to be similar to the cyberattack on the French government in the run up to the G20 Summit in February 2010. That assault involved malware and targeted email, with some of the related stolen information redirected to China.
Commission administration spokesman Antony Gravili said officials would not speculate on the source of the attacks in such a sensitive security matter. He did, however, confirm that the attackers targeted the information of some Commission officials, in particular at the External Action Service, the body's foreign diplomatic arm.
"We are already taking urgent measures to tackle this. An inquiry's been launched. This isn't unusual as the Commission is frequently targeted," said Gravili. He added that there was no concrete evidence that the attack is linked to the EU summit.