FRANKFURT AM MAIN (AFP) - German sportswear maker Adidas has warned some Americans who shopped with the company online that their data may have been stolen.

"On June 26, Adidas became aware that an unauthorised party claims to have acquired limited data associated with certain Adidas consumers" who shopped on its United States website, the group said in a statement on Thursday (June 28).

While hackers may have gained access to contact details, usernames and encrypted passwords, Adidas said there was "no reason to believe" they stole credit card information or fitness data.

The firm "immediately began taking steps to determine the scope of the issue and to alert relevant consumers", it added, saying it was working with "leading data security firms and law enforcement authorities".