Files with fantom file extension can be usually encountered as encrypted files affected by the Fantom ransomware.
FANTOM file extension - Fantom ransomware affected data
What is fantom file? How to open fantom files?
File type specification:
The fantom file extension seems to be mainly related to a one of the ransomware, this particular one labeled as Fantom.
This ransomware masks itself as critical update for Windows to hide its true purpose.