Foreign Secretary Dominic Raab's mobile number has been available online for years, prompting fresh questions for the security services.
The Foreign Office confirmed that Mr Raab's number and other private information had been freely available since before 2010 - but it has now been taken down.
The top Tory's details appeared to have been online since before he became an MP in 2010, according to The Guardian.
A Foreign Office spokesman said: "Private information was wrongly retained online, before the Foreign Secretary's appointment.
"Once we were made aware, we had it removed immediately. Most of it was out of date, and no security was compromised."
It comes after it was revealed that Boris Johnson's personal number had been online for 15 years.
The PM's number was at the bottom of a think tank press release from 2006 when he was shadow higher education minister, prompting fears he had left himself vulnerable to hostile states.
Civil service chief Simon Case had already reportedly told Mr Johnson to change his number as it was too widely known.
It has since been disconnected.
Shadow Foreign Secretary Lisa Nandy blasted the Government for taking a lax approach to protecting national security.
“This is a staggering lapse in security from a foreign secretary who, only last month, was lecturing Nato allies about the cybersecurity threat posed by authoritarian regimes," she told the Guardian.
“It is typical of the government’s approach that when it comes to national security and defending democracy they say one thing but do another.
"This should be the subject of an investigation. Both the prime minister and foreign secretary have failed to protect their own phones.
"How can we be assured they aren’t as careless with sensitive intelligence and diplomatic cables too?”
It comes amid a row over ministers' use of their private emails after ex-Health Secretary Matt Hancock was said to have used his personal account to conduct Government business.
Ex-No10 aide Dominic Cummings has also published sensitive WhatsApp messages between himself and the Prime Minister at the height of the pandemic.
