Encryption / Description Alphanumeric 16 digits

[eluser]mddd[/eluser]
Also important: if you use a hash, you have more control. The hash is only the "key" to the information. It does not contain the information itself.
You can check additional things in the background: maybe the hash was given to a user who no longer has permission to view the information? Maybe the hash is only valid for a certain amount of time? Bottom line: you can check things. If the supplied number IS the information, you don't have so much control.