What is this hacker trying to do?
If you do a search for:
you will see a lot of examples of an attempted hack along the lines of:
1) declare @q varchar(8000) select @q = 0x57414954464F522044454C4159202730303A30303A313527 exec(@q) --
What is exactly is it trying to do? Which db is it trying to work on? Do you know of any advisories about this?
Answer
He is testing your server for SQL Injection, specifically this is a robust test that will work even if its Blind SQL Injection. Blind SQL Injection is when an attacker is able to execute SQL however, there isn't a viewable response. If the http request takes at least 15 seconds the attacker will know that he can execute SQL, and that your running MS-SQL. After this attack he will follow it up with a xp_cmpdshell() to infect your server.