A House of Commons spokeswoman said that "the Houses of Parliament have discovered unauthorised attempts to access parliamentary user accounts.
"We have systems in place to protect member and staff accounts and are taking the necessary steps to protect our systems.
"Parliament has disabled remote access to protect the network," she said.
The threat follows reports in British media, including the Times, that hackers were selling passwords for MPs online.
Liberal Democrat lawmaker Chris Rennard tweeted that there was a "cyber security attack on Westminster; Parliamentary e-mails may not work remotely."
The National Crime Agency said it was "aware of a possible cyber incident affecting parliament".
International Trade Minister Liam Fox told ITV News said it was a "warning to everyone we need more security and better passwords".
Fox told the BBC: "We know that our public services are attacked so it is not at all surprising that there should be an attempt to hack into parliamentary emails".
A global ransomware attack last month hit hundreds of thousands of computers, including hospitals in Britain that were forced to shut down, divert emergency cases and postpone operations.
The so-called WannaCry ransomware locked access to user files and in an on-screen message demanded payment of $300 (275 euros) in the virtual currency Bitcoin in order to decrypt the files.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)