Static signatures are increasingly pointless as malware is rebuilt often.

Heuristics don't work against ransomware because they act like a well behaved program. Search for files, open file, overwrite file. All could be done as non-privileged user.

Ransomware is truly scary but the proper advice is: 1. Don't run untrusted software 2. Proper backups (e.g. not just a mirror) 3. Proper permissions on network drives that are mapped. Ransomware is devastating to small offices.