-1" OR 5*5=25 --

That looks like a classic SQL injection payload. Here’s what it does and why it’s a problem:

• The -1" part is meant to close a string literal in a SQL query.
• OR 5*5=25 is a boolean condition that evaluates to true (25 = 25).
• The -- starts a SQL comment, so the rest of the query is ignored.

If a web app builds a query by concatenating user input, this can transform something like: SELECT * FROM users WHERE username = 'USER_INPUT'; into something like: SELECT * FROM users WHERE username = "-1" OR 5*5=25 --'; which effectively makes the WHERE clause true for all rows, potentially bypassing authentication or leaking data.

Defenses (best practices):

• Use parametric/prepared statements everywhere (don’t concatenate user input into SQL).
• Use a safe ORM or query builder that binds parameters.
• Validate and sanitize inputs; prefer whitelisting (e.g., allow only alphanumeric usernames).
• Apply least-privilege database accounts (no passwords or admin rights for typical app users).
• Disable multiple-statement execution if your driver supports it.
• Consider a Web Application Firewall and proper error handling that doesn’t reveal DB details.

If you want, I can show concrete examples in a language you’re studying (e.g., Python with psycopg2, Java with JDBC) or give a quick practice exercise on writing secure queries.