If you have been using MyFitnessPal from Under Armour, change your password immediately. On March 25 Under Armour learned that usernames, email addresses and hashed passwords were taken from about 150 million user accounts.
The good news is the passwords were hashed or scrambled and will need to be decoded before they can be used. The bad new is, the thieves may use phishing emails to acquire your password directly instead of doing the hard work of decoding it. Change your password directly in the app or through their website instead of using a link in an email.
If you use your MyFitnessPal password for other apps or websites, make sure you change those passwords as well.