-1' OR 5*5=25 or 'mg6zfHtx'='

That looks like a classic SQL injection payload.

What it’s doing

• It tries to break out of a string literal in a SQL query and inject a tautology (a condition that’s always true).
• 5*5=25 is true, so if this input gets concatenated into a WHERE clause, the injected condition can make the query return data (or bypass authentication) regardless of the real input.
• The segment 'mg6zfHtx'='' is another attempt to keep the overall condition valid.

Why this is a problem

• If user input is directly concatenated into SQL, an attacker can alter the query logic.
• This can lead to bypassing login, data leakage, or data corruption.

Defensive fixes (what you should know for exams and real apps)

• Use parameterized queries (prepared statements) instead of string concatenation.
• Validate and constrain inputs (type checks, length limits) before using them in queries.
• Use an ORM or safe database API that automatically parameterizes inputs.
• Avoid executing multiple statements in one query (disable stacked queries if the DB/driver allows).
• Apply least privilege to the DB user accounts (no more permissions than needed).
• Do not reveal detailed DB errors in responses; log them server-side.

Examples

Python (using parameterized queries)

• Vulnerable pattern: cursor.execute("SELECT * FROM users WHERE username = '" + username + "' AND password = '" + password + "'")
• Safe pattern: cursor.execute("SELECT * FROM users WHERE username = ? AND password = ?", (username, password))

Java with JDBC

• Safe: PreparedStatement ps = conn.prepareStatement("SELECT * FROM users WHERE username = ? AND password = ?"); ps.setString(1, username); ps.setString(2, password); ResultSet rs = ps.executeQuery();

If you’re studying for an exam, focus on:

• Why concatenating user input into SQL is dangerous.
• How parameterized queries prevent injection.
• Additional defenses (input validation, least privilege, error handling).

If you want, I can tailor examples to a specific language or framework you’re studying.