https://www.bleepingcomputer.com/news/security/phishing-attacks-unusual-file-attachment-is-a-double-edged-sword/

A threat actor uses an unusual attachment to bypass security software that is a double-edged sword that may work against them.

As secure email gateways and security software become more advanced and adapt to ever-changing phishing campaigns, threat actors resort to more unusual file formats to bypass detection.