-1" OR 5*5=25 --

Short answer: it’s a classic SQL injection payload.

What it does (in a typical login or similar query)

• The -1" tries to break out of a string literal in the SQL query.
• OR 5*5=25 is a boolean expression that evaluates to true.
• The -- starts a comment, so the rest of the original query is ignored.

Effect: if the input is concatenated into a SQL statement, the WHERE clause can become something like: WHERE username = '-1' OR 5*5=25 -- ... which is effectively always true, so authentication (or the intended check) can be bypassed.

Why this matters

• It exploits improper handling of user input in SQL queries.
• It can lead to unauthorized access, data leakage, or data manipulation.

How to defend (defensive, exam-ready guidance)

• Use parameterized queries (prepared statements) everywhere:
  • Do not build SQL by string concatenation with user input.
  • Example concept:
    • SELECT * FROM users WHERE username = ? AND password = ?
    • Bind username and password as parameters, not as part of the SQL string.
• Validate and sanitize inputs, and implement a strict allowlist for expected formats (e.g., usernames).
• Use an ORM or database library that automatically parameterizes queries.
• Disable or restrict multi-statement execution if your DB supports it.
• Apply the principle of least privilege: the app’s DB user should have only the minimal rights needed.
• Avoid including raw error messages in responses; they can reveal query structure.
• Consider using stored procedures with proper parameter binding, and consider input validation inside the database where appropriate.
• Keep frameworks and libraries up to date with security patches.

If you want, tell me which DB (MySQL, PostgreSQL, SQL Server, etc.) and which language you’re using, and I can show concrete safe code examples in that setup.