Under Armour, which owns health and fitness app MyFitnessPal, has confirmed that the personal details of 150 million of its users has been stolen.

The data includes names, email addresses and encrypted passwords.

Under Armour did not say how the breach occured, but is advising its users to change their passwords immediately.

"On March 25, the MyFitnessPal team became aware that an unauthorised party acquired data associated with MyFitnessPal user accounts in late February 2018," Under Armour announced in a press release.

"The company quickly took steps to determine the nature and scope of the issue and to alert the MyFitnessPal community of the incident.

"The affected data did not include government-issued identifiers (such as Social Security numbers and driver's license numbers), which the company does not collect from users.

"Payment card data was also not affected because it is collected and processed separately.

"Four days after learning of the issue, the company began notifying the MyFitnessPal community via email and through in-app messaging.

"The notice contains recommendations for MyFitnessPal users regarding account security steps they can take to help protect their information."