-1" OR 5*5=25 --

This looks like a classic SQL injection payload.

What it does (in brief):

• The -1" part attempts to break out of a string literal in a SQL query.
• OR 55=25 adds a condition that is always true (55 equals 25).
• -- starts a comment, so the rest of the original query is ignored.
• If the application builds SQL by concatenating user input, this can cause the WHERE clause to be true for all rows, potentially bypassing authentication or exposing data.

Defenses and best practices:

• Use parameterized queries (prepared statements) with bound parameters. Do not concatenate user input into SQL strings.
• Avoid dynamic SQL; use stored procedures that separate code from data when appropriate.
• Implement input validation and strict allow-lists (only accept expected values/formats).
• Enforce least privilege for the application database user (no broad SELECT/UPDATE rights beyond what’s needed).
• Handle errors safely; don’t reveal raw database errors to users.
• Consider using ORMs or query builders that automatically parameterize queries.
• Employ Web Application Firewall (WAF) and security scanners in a controlled lab environment to test defenses.
• Practice in ethical, legal environments (lab machines, DVWA/WebGoat/OWASP Juice Shop) to study both attacks and mitigations.

If you’re preparing for an exam, you can illustrate the contrast with a safe example:

• Vulnerable: SELECT * FROM users WHERE username = 'USER_INPUT';
• Safe: SELECT * FROM users WHERE username = ?; with the user input bound as a parameter.

If you want, tell me your exam topic and I can tailor a concise defense answer or a short defensive code example in a specific language.