The best practice for password security among the given options is changing passwords often.
Here’s a brief explanation of the other options:
- Using the same password for many sites: This is not recommended because if one site is compromised, all accounts using that password are at risk.
- Sharing passwords with trusted friends: This can lead to security vulnerabilities, even with trusted individuals.
- Using real words in passwords: This is generally discouraged since predictable passwords can be easily guessed or cracked using dictionary attacks.
Thus, the correct answer is changing passwords often.