I've added an About page.
http://guid2steamid.pw/about
The user Dark over at http://forum.dayz-ast.com/ created a bruteforce script which start at SteamID: 76561198300000000 , then hashes it with md5(the normal/right way) and then compares it with the guid put in, if wrong it subtracts steamid by 1 and tries that one. With bruteforce it takes an average of 1.5 hours for 1 guid, but it takes the same time for 150 guid's too.
Then I decided to make a simple rainbow table, here are the 3 first lines of the big file.
69898442674896b544cba6b0c1915315 76561198370000000
ef7844fcd61c8c018790e8380547e138 76561198369999999
742124c393a4d4efa1df1c4baa61022c 76561198369999998
The file contains 470.000.000 SteamID's using 24,4GB
Instead of using cpu power by hashing steamid's to md5(guid) this searches a big file for the correct line.
The only bad thing about this design is doing multiple guid's, as i said above. Bruteforce takes the same amount of time depending of CPU power, but with rainbow table 150 guid takes 3 hours and 40 minutes
Sorry for long reply :)
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