https://www.bleepingcomputer.com/news/security/compression-file-formats-of-the-past-come-haunting-in-spam-campaigns/

Some ancient filetypes are making a comeback due to unwanted attention from cybercriminals looking for more effective ways to hide malware distributed through spam campaigns.

Specifically, two archives that today are mostly seen on computers of nostalgic geeks or professionals working with old files, have been used recently in spam campaigns to deliver info-stealing malware or a backdoor.