Signal messaging app and its security

When the White House disclosed that senior US officials were using the free messaging app Signal for a private group chat, it made headlines.

Jeffrey Goldberg, the chief editor of the Atlantic, was among the group that inadvertently discussed plans for an attack against the Houthi group in Yemen.

There has been a massive backlash after Democratic Senate leader Chuck Schumer called it “one of the most stunning” military intelligence leaks in history and called for an investigation.

However, what is Signal in reality, and how safe were the communications between the top politicians on it?