is it possible to get server side Flash APIs, to stop games from being easily hacked into saying 999999 highscore
Depends on the game, who coded it, how they coded it, etc. If it was coded poorly without much security in mind then it'll be hacked, otherwise it will not.
if you would be able to up security for any game PM me, i really have no idea where to start on this :S
You would have to have the original FLA for the flash so that a flash developer could edit it as needed. The server side can depend on whatever scripting language was used. I'm a PHP/MySQL developer, but not a Flash developer.
It can be quite laborious and dependent on the way the files are programmed and also your hosting environment.
Flash file can be reverse engineered to see how it saves game data on the server. If server has no rules on how the data is saved then it can be changed easily.