[Phytrix]

If you have a custom crypter and you hire the right person, the crypter will be damn near permanently FUD.

As for making it, be sure to encrypt the unencrypted data back into the stub with a different key each time.

No such thing as a perm or near perm crypter. You infect someone, they scan their system properly (looking at logs), and then it's not FUD anymore.
Even if you make the malware meta or polymorphic, it won't make it perm or near perm.

Yes, if a file is found to be a virus, it can be removed. But then if a file with a completely different signature with the same virus is introduced, so long as the stub keeps to functions with legitimate use in other programs, the new file will be UD.

The AV/AM companies look at the programming and then make it recognise all variations of that virus (using the algorithms) as malicious.