Facebook Inc.'s first "security tip" for users is, "Don't use your Facebook password anywhere else online." If only Chief Executive Mark Zuckerberg had heeded that advice. Mr. Zuckerberg's Twitter Inc. and Pinterest Inc. accounts were taken over in recent days because he reused a password: "dadada," according to a person familiar with the matter. The password had appeared last month in a database of more than 100 million usernames and passwords stolen in 2012 from LinkedIn Corp., the person said. Mr. Zuckerberg appears to have reused "dadada" to log into Twitter and Pinterest, allowing hackers to take over those accounts. The age-old advice to not re-use passwords is particularly timely at the moment. Beyond the LinkedIn theft, there were also recent leaks of 360 million email addresses and passwords belonging to users of MySpace.com. Since May, the website Leakedsource.com, which sells access to the stolen information, has added close to one billion records to its database, a