State two issues with only using usernames and passwords in an authentication system.

Using only usernames and passwords for authentication, while common, has several significant security weaknesses: 1. **Human Factor - Weak Passwords:** Users frequently create weak, short, or easily guessable passwords (like "password123" or a pet's name) to make them easier to remember. They also tend to reuse the same password across many different websites. This makes them vulnerable to guessing or brute-force attacks. 2. **Susceptibility to Theft:** Passwords can be stolen through various means. **Phishing** attacks trick users into entering their credentials on fake websites. **Data breaches** at companies can expose databases of usernames and passwords. **Spyware** or **keyloggers** installed on a user's computer can capture keystrokes and steal passwords directly.