: Attackers use NULL to figure out exactly how many columns the original database table has. If the number of NULL s matches the columns, the page loads; if not, it crashes.

The text ') UNION ALL SELECT NULL,NULL...-- is a malicious payload used to test for vulnerabilities in a database.

Modern web development has largely moved past this threat using a technique called (or Parameterized Queries). Instead of letting user input mix directly with the code, the database is told: "Treat this input strictly as text, no matter what symbols are inside it."

: This attempts to "break out" of the developer’s intended code by closing a data field and a function.

If a website is vulnerable to this, an attacker doesn't just stop at NULL . They eventually replace those NULL s with commands to extract sensitive info—like your —and display them right on the screen where the "Keyword" results should have been. How Developers Stop This