“As a result, some Members of Parliament (lawmakers) and staff cannot access their email accounts outside of Westminster,” it said, adding that IT services at Parliament itself are working normally.
It was not immediately clear how many people were affected or what the extent of the damage was.
An email sent all those affected described a “sustained and determined attack on all parliamentary user accounts in an attempt to identify weak passwords,” according to The Guardian newspaper. “These attempts specifically were trying to gain access to our emails.”
Liberal Democrat Chris Rennard said on Twitter that urgent messages should be sent by text message because parliamentary emails may not work remotely.
The National Cyber Security Center and the National Crime Agency are looking into the incident.
Liam Fox, Britain’s International Trade Secretary, told ITV News that the attack was “a warning to everyone: We need more security and better passwords. You wouldn’t leave your door open at night.”