Under Armor has uncovered that, according to data of 150 million, it is one of the biggest hacks in The history has suffered users of the MyFitnessPal diet and fitness app were compromised in February.
According to Reuters, Under Armor shares fell 3% after the close.
"On March 25, the MyFitnessPal team became aware of an unauthorized party data that was linked to MyFitnessPal user accounts at the end of February 2018," the company wrote in a statement. "The company quickly took steps to identify the nature and scale of the issue and inform the MyFitnessPal community about the incident."
The stolen data includes account usernames, email addresses, and encrypted passwords for the MyFitnessPal app and website. Social security numbers, driver license numbers and payment card details were not compromised.
The company said the investigation is ongoing, but so far about 150 million user accounts have been affected by the biggest violations of the year, one of the top five in history. Under Armor stated that they did not know the identity of the unauthorized party.
MyFitnessPal users are prompted to change their passwords immediately and to check their accounts for suspicious activity.
Under Armor bought MyFitnessPal in 2015 for $ 475 million. The app and website are part of the Connected Fitness Division, which made 1.8 percent of Under Armor's $ 5 billion in total revenue last year.
While the breach did not include any financial data, theft of large amounts of data is still much to gain amounts of e-mail addresses. In fact, e-mail addresses retrieved in 2014 in an attack involving data from around 83 million JPMorgan Chase customers were later used in pump-and-dump systems to increase stock prices.
"We continue to monitor suspicious activity and coordinate with law enforcement agencies," Under Armor told its customers. "We continue to make improvements to our systems to detect and prevent unauthorized access to user information."