Arstechnica reports on the discovery of signed malware designed for surveillance on the Mac laptop of an Angolan activist.
The malware was a trojan that the activist obtained through a spear phishing email attack. The news here is that the malware was signed with a valid Apple Developer ID.
The idea is that having all code signed should substantially reduce the amount of malware on the platform. This works because creating a valid Apple Developer ID requires significant effort, and may expose the identity of the hacker unless they take steps to hide their identity. This is not trivial as the Developer ID requires contact information and payment of fees.
The second advantage of signed code is that the Developer's certificate can be quickly revoked, so the software will be detected as invalid and automatically blocked on every Mac world wide. This limits the amount of damage a given Malware can do, and forces the attacker to create a new Apple Developer ID every time they are detected.
This has been seen to work fairly well in practice, but it is not perfect. If a target is valuable enough, a Developer ID can be set up just to go after that one person or small group. The malware is targeted to just them, so the likelihood of detection is low. In this case, it would continue to be recognized as a legitimates signed valid application for a very long time.
In the case of the Angolan activist, it was discovered at a human rights conference where the attendees were learning how to secure their devices against government monitoring.