Files with serp extension can be most often found as files which have been affected by the Serpent ransomware.
SERP file extension - Serpent (variant) ransomware affected file
What is serp file? How to open serp files?
File type specification:
File extension serp is also used for one of the variant of Serpent ransomware. Much like other ransomware, it encrypts users files and demands bitcoins in exchange for the decryption. The notes are left in the README_TO_RESTORE_FILES.txt file.