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

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

: This command tells the database to combine the results of the original legitimate query with the results of a new query. {KEYWORD}') UNION ALL SELECT NULL,NULL,NULL,NULL,NULL-- DyYf

: 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). The string you provided is a classic example of a