CompTIA Security+ Question J-70

After Matt, a user, enters his username and password at the login screen of a web enabled portal, the following appears on his screen:
`Please only use letters and numbers on these fields’
Which of the following is this an example of?

A. Proper error handling
B. Proper input validation
C. Improper input validation
D. Improper error handling

Answer: B

Input validation is an aspect of secure coding and is intended to mitigate against possible user input attacks, such as buffer overflows and fuzzing. Input validation checks every user input submitted to the application before processing that input. The check could be a length, a character type, a language type, or a domain.