Blocking file names with 20 + hex characters

[MRB]

I'm trying to block posts with 20+ hex characters as the file name, I've have several unsuccesful tries, mainly due to my lack of knowledge of regular expressions. (*nix was a long while back for me and never a mainstream part of work)

Any help gladly recieved.

Thanks, Malcolm.

[Smite]

[a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9][a-f0-9] would probably work

[MRB]

Thanks. I'll give that a try.