Clearly what has happened to CZ is not a vulnerability in Signal, he has probably had his phone hacked and had access to his data or there is a mole.
However, it is important to understand the flaws in Signal that can lead to targeting:
- Centralized servers
- Metadata collection
- Not anonymous, requires a phone number.
Simplex solves all these problems:
- Decentralized and you can set up your own receiving server or as many as you want for each contact.
- No user IDs, a new identity is generated for each contact or group, which makes metadata collection complicated.
- It is anonymous.
