[artinmg]

Well you can’t necessarily, because who’s to say what various methods they’ve discovered. However, if we were to use the most famous recent example that relied on an unknown sender transmitting a GIF containing the compromise, Signal does have some additional protection in that it doesn’t receive messages from unknown senders by default. Rather the recipient must accept the message explicitly.

[Sharlin]

Honestly, even after accepting the message there should be another confirmation step before viewing any and all non-textual content.