If you found this in your website logs, comment sections, or form submissions, it means an or a person is testing your site for security flaws. They are looking to see if your application is "injectable," which could allow them to steal data or bypass login screens. How to stay safe To prevent these types of attacks, developers should:
: This is a SQL comment. It tells the database to ignore everything that follows it, effectively neutralizing the rest of the original, legitimate code.
: The attacker is trying to determine how many columns the original database table has. If the number of NULL values doesn't match the number of columns in the original query, the database will return an error. By adding or removing NULL s, an attacker can find the exact table structure.
: This attempts to "break out" of a standard text input field in a web application by closing the developer's intended SQL query quote early.
: This is the core of the attack. It tells the database to append the results of a second query to the results of the first one.