-1' OR 5*5=26 --

That looks like a simple SQL injection payload. Here’s the gist:

• -1' : tries to terminate a string literal in a SQL query.
• OR 5*5=26 : injects a boolean expression. If the surrounding query is such that this OR condition can influence the WHERE clause to evaluate to true, it can alter or bypass logic (e.g., authentication).
• -- : SQL comment marker. It comments out the remainder of the line, effectively ignoring any trailing SQL that the attacker can’t predict.

Note: 5*5=26 is mathematically false (25 ≠ 26). Whether this injection works depends on the original query and context. The key idea is the attacker’s attempt to break out of string context and inject an OR condition, then hide the rest of the query with a comment.

How to defend (exam-ready essentials):

• Use parameterized queries / prepared statements for all user input.
• Avoid building SQL by concatenating strings with user data.
• Use least-privilege database accounts (no unnecessary rights).
• Validate and whitelist inputs where feasible (and do not rely on escaping alone).
• Disable verbose database error messages; log and monitor for injection-like patterns.
• Consider using ORM tooling or stored procedures with parameters.

If you want, I can show a concrete vulnerable vs. safe example in a language you’re studying (e.g., Python with SQLite, Java with JDBC, PHP with PDO) to illustrate the difference. Do you want that? Also, would you like a quick exam-style question on this topic?