https://www.bleepingcomputer.com/news/security/emotet-malware-now-distributed-in-microsoft-onenote-files-to-evade-defenses/

The Emotet malware is now distributed using Microsoft OneNote email attachments, aiming to bypass Microsoft security restrictions and infect more targets.

Emotet is a notorious malware botnet historically distributed through Microsoft Word and Excel attachments that contain malicious macros. If a user opens the attachment and enables macros, a DLL will be downloaded and executed that installs the Emotet malware on the device.