[SEMI-OT] Making secure flash high scoring?

Sorry for the semi-ot post, but this is both a flash and php question, and I'm not a member of any flash lists, so I decided to post it here. Anyway, I have a game site with virtual pets, virtual shops, user accounts, etc. One feature request I get alot is flash games. I could find someone to make them, but I'm not sure about ways of making the score submitting secure. Any thoughts? -- The above message is encrypted with double rot13 encoding. Any unauthorized attempt to decrypt it will be prosecuted to the full extent of the law.