: These are comment characters used to "comment out" the rest of the original, legitimate SQL query so it doesn't cause a syntax error. Vulnerability Report
: This attempts to close an existing single-quote string and provide a non-existent ID so that the primary query returns no results. -7728') UNION ALL SELECT 34,34,34,34#
The string you provided appears to be a , specifically an attempt to perform a UNION-based attack to extract data from a database. What This String Does : These are comment characters used to "comment