If you receive an email from Netflix or Facebook asking you to change your password because it matches a credential from an older security breach, you may want to heed its advice. Cybersecurity expert Brian Krebs says some big companies, including the streaming service and the social network, tend to go through data from other websites' security breaches to look for log-ins that match their users'. They then force those users to change the passwords they reused to keep them safe. If you'll recall, hackers recently sold the millions of log-in combinations they stole from LinkedIn, Tumblr and MySpace a few years ago.