The Signal messenger and protocol.

An internal memo from the Prime Minister was leaked in which she asks cabinet members to stop using mainstream messaging apps and use Olvid (an app developped by a French startup) instead. She does not mention Signal specifically, but the implication is that other messaging apps have security flaws.

Meredith stresses that one may very well prefer one app to another based on different threat models, but that it is not fair to imply that an app is not secure without presenting proof.