No specific threat from a hostile state has been identified, but rather the alert informed about the voting process and its vulnerabilities.
Because of the concerns, the Conservative Party has now been forced to scrap plans to let members change their vote for the next leader at a later stage in the process, writes The Telegraph.
The sudden change means postal ballots have not yet been issued to the approximately 160,000 Tory members who will choose Boris Johnson's successor.
Ballots were due to be sent out from Monday, but members have now been told they could arrive as late as August 11.