Exploiting an SQL Inject attack involves solving a puzzle that is a cross between Hangman and 20 Questions. It needs a little understanding of SQL and a great deal of cunning.
Try your Hacking skills against this test system. It takes you through the exploit step-by-step.
The SQL Injection attack allows external users to read details from the database. In a well designed system this will only include data that is available to the public anyway. In a poorly designed system this may allow external users to discover other users' passwords.