GEN:SID 1:683
Message MS-SQL sp_password - password change
Summary This event is generated when a command is issued to an SQL database
server that may result in a serious compromise of the data stored on
that system.
Impact Serious. An attacker may have gained administrator access to the system.
Detailed Information This event is generated when an attacker issues a special command to an
SQL database that may result in a serious compromise of all data stored
on that system.

Such commands may be used to gain access to a system with the privileges
of an administrator, delete data, add data, add users, delete users,
return sensitive information or gain intelligence on the server software
for further system compromise.

This connection can either be a legitimate telnet connection or the
result of spawning a remote shell as a consequence of a successful
network exploit.
Affected Systems  
Attack Scenarios Simple. These are SQL database commands.
Ease of Attack Simple.
Corrective Action Disallow direct access to the SQL server from sources external to the
protected network.

Ensure that this event was not generated by a legitimate session then
investigate the server for signs of compromise

Look for other events generated by the same IP addresses.
Additional References Microsoft MSDN:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/tsqlref/ts_sp_pa-pz_5x44.asp