-1" OR 5*5=25 or "fppgDt0y"="

That string looks like an SQL injection payload. It’s trying to break out of a quoted value and insert a tautology (an always-true condition) into a SQL query.

What the payload is doing

• -1" ends a string literal in many SQL contexts.
• OR 55=25 adds a condition that is true (since 55 equals 25).
• OR "fppgDt0y"=" adds another comparison, but the important part is the OR 5*5=25, which can turn a WHERE clause into something that’s always true.
• If injected into a vulnerable query like: SELECT * FROM users WHERE username = '$input' AND password = '$pass', the injected part can make the WHERE clause evaluate to true for many or all rows, potentially bypassing authentication or leaking data.
• The trailing =" is incomplete in isolation, so the exact effect depends on the surrounding query and how the input is concatenated.

How to defend (exam-safe guidance)

• Use parameterized/prepared statements for all queries. Do not interpolate user input directly into SQL.
  • Example (generic): SELECT * FROM users WHERE username = ? AND password = ?
  • Bind user inputs as parameters, not as string concatenation.
• Validate and sanitize input:
  • For numeric fields, reject non-numeric input.
  • Enforce expected formats (length, character set).
• Principle of least privilege:
  • The DB user used by the application should have only the permissions needed (e.g., SELECT/UPDATE on specific tables, not admin rights).
• Use an ORM or database library that automatically handles escaping and parameterization.
• Enable defensive features:
  • Disable multi-statement execution if your driver supports it.
  • Use strict error handling and avoid exposing raw SQL errors to users.
• If you’re testing, do so in a legal, controlled environment (e.g., DVWA, OWASP WebGoat) and with permission.

A tiny safe example (conceptual)

• Vulnerable: SELECT * FROM users WHERE username = 'USER' AND password = 'PASS';
• Safe: SELECT * FROM users WHERE username = ? AND password = ?; // and bind USER, PASS as parameters

If you want, tell me the language and DB you’re studying for, and I’ll tailor a concrete example showing both a vulnerable version and a fixed, secure version.