-1" OR 5*5=25 --

That looks like a classic SQL injection payload.

What it does (conceptually):

• The -1" tries to close a quoted string in an SQL statement.
• OR 5*5=25 is a tautology (true), so if injected into a WHERE clause it can cause the condition to always be true.
• The -- cancels the rest of the line (comment), so any trailing SQL you didn’t intend to expose is ignored.

In short: if an application builds SQL by concatenating user input, this kind payload can bypass checks or alter results.

Defensive ideas (exam-ready, defense-in-depth):

• Use prepared statements / parameterized queries (placeholders for user data; never concatenate strings).
  • Example (pseudo):
    • Python/psycopg2: cursor.execute("SELECT * FROM users WHERE username = %s", (username,))
    • Java: PreparedStatement with ? parameters
• Avoid dynamic SQL; use ORM or safe query builders.
• Validate and sanitize inputs, but don’t rely on escaping alone.
• Implement least-privilege database accounts (no write access where not needed).
• Use proper error handling to avoid leaking SQL details.
• Consider a Web Application Firewall (WAF) and logging/security tests (in a lab) to detect such payloads.
• Regularly test with safe security tests (in a consented environment) to verify defenses.

If you want, I can show a concrete before/after example in a language you’re studying (e.g., Python, Java, Node.js) to illustrate how parameterization prevents this payload from ever affecting the query. Also, I can provide a quick checklist for SQLi prevention on exams.