haha, tim ra roi, day chinh la cai minh can

If you had such a site with lots of Flash files, how would you protect against hotlinking? lighttpd’s solution, applicable to any file type, is mod_secdownload. You write a function (examples in the link include PHP and Ruby) to generate a special URL, and the module cracks the URL to permit access to a given file for a given amount of time.

http://www.onlamp.com/pub/a/onlamp/2007/04/05/the-lighttpd-web-server.html?page=last#thread

ps: dang dung ubuntu nen ko co tieng Viet, keke