-1' OR 3*2>999 --

It looks like a basic SQL injection payload. Here’s a high‑level, non-operational explanation and some defensive tips:

What this string tries to do (conceptually)

• It ends a quoted string in a SQL query with a trailing single quote: -1'
• Then injects OR 3*2>999 as an additional condition
• The expression 3*2>999 is 6>999, which is false
• The double dash -- starts a comment, so the rest of the original query is ignored
• In an insecure query, this could alter the WHERE clause logic (potentially bypassing checks or returning different results)

Important safety note

• Don’t attempt to test or exploit SQL injections on systems you don’t own or don’t have explicit permission to test. It’s illegal and harmful.

Defensive measures (how to prevent this)

• Use parameterized queries (prepared statements) instead of string concatenation for user input.
  • Example concept: SELECT * FROM users WHERE username = ? AND password = ? (bind values safely)
• Avoid dynamic SQL. Use ORM or well‑defined query builders.
• Validate and type-check inputs; enforce expected data types and lengths.
• Least privilege for the database user (no rights beyond what the app needs).
• Proper error handling and do not reveal raw SQL errors to users.
• Consider input normalization and escaping only as a last resort (not a replacement for parameterization).
• Use a Web Application Firewall (WAF) as an additional layer, but don’t rely on it alone.

If you’re preparing for exams and want, I can show examples of safely querying various languages (Python, Java, Node.js) using parameterized queries and how that neutralizes this kind of payload.