I stumbled upon a fun little sql injection in playfoursquare the other day. I notified them but have not heard back, but it appears it has been addressed so here are the details.

     It was possible to inject specially crafted SQL into the cookie "cookieCityID"
     which provides 

     If you set the cookie to the value below the query will take roughly 5-7
     seconds to return with this "True" condition (1=1).

     (SELECT IF(1=1,BENCHMARK(1000000,SHA1(1)),0))

     If you change the logic condition to 1=0 (False) the query returns
     immediately demonstrating that blind SQL injection is possible.

     (SELECT IF(1=0,BENCHMARK(1000000,SHA1(1)),0))

III. REFERENCES
     [1] - http://playfoursquare.com

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