{keyword}') Union All — Select Null,null,null,null,null-- Dyyf

The string you provided is a classic example of a . Specifically, this is a Union-based SQL injection attempt.

: The attacker is trying to determine how many columns the original database table has. By providing five NULL values, they are testing if the original query also returns five columns (the number of columns must match for a UNION to work). {KEYWORD}') UNION ALL SELECT NULL,NULL,NULL,NULL,NULL-- DyYf

If you found this in a product review section, a log file, or a search bar, it means someone (or an automated bot) was . They were checking if the site properly "sanitizes" user input or if it is vulnerable to data theft. The string you provided is a classic example of a

: This command tells the database to combine the results of the original legitimate query with the results of a new query. By providing five NULL values, they are testing

: This part attempts to "break out" of a predefined search query. The ') is used to close a string literal and a parenthesis in the backend code, allowing the attacker to append their own commands.