Book excerpt: A white hat hacker is a computer security specialist who breaks into protected systems and networks to test and asses their security. White hat hackers use their skills to improve security by exposing vulnerabilities before malicious hackers (known as black hat hackers) can detect and exploit them. Although the methods used are similar, if not identical, to those employed by malicious hackers, white hat hackers have permission to employ them against the organization that has hired them.