Wireless connection between two Arduino's

Hi guys and girls! I am currently making my exam project for my education, and I need a little help with it.. See, what i am trying to make is a wireless post indicator, and if that doesnt explain enough, it is going to be a wireless connection between two arduino boards, where the one that sits in the mailbox tells the one sitting in the house there is mail, and it has to be wireless. Now, for equipment, i have two arduino uno rev3, two WiFly shields (http://www.seeedstudio.com/wiki/Wifi_Shield_V1.1) and thats about it. My problem comes when i have to send a signal from the first to the second arduino, i have literally no idea how. I have connected them with Ad Hoc so it doesnt require a router. I have read that i have to use TCP because UDP is not secure package delevery, i dont know if that is true. So, if possible, please help! :D

Jonas Strand aka. Strand_DK

So, if possible, please help!

If you search for Arduino mailbox notifier you might get a few hundred thousand ideas!