A new denial of service attack was recognized last week by Malwarebytes, a manufacturer of antivirus software. Its effect is quite unusual: it freezes user machines by generating, in an uninterrupted way, windows for composing new emails from Safari.
According to the researchers, this is done based on a simple macOS bug, which allows the attacker to take control of the Mail and Safari processes that are open on the user's machine. From them, drafts of emails are generated that cannot be closed and / or sent, until the system crashes completely.
The practice is quite common in malware for Windows and is being distributed by various websites and malicious senders. In addition to the trivial precautions when validating incoming emails (as well as links, before clicking), it is recommended that users update to the latest version of macOS Sierra (10.12.2), which is not the most affected by this attack.