Hackers stole certain confidential data from McDonald's Corp. customers in the United States, South Korea and Taiwan, the company said Friday.

The burger giant said it has hired external experts to examine the authorized breach on its internal systems, that exposed customer emails, phone numbers and addresses for delivery in South Korea and Taiwan.

McDonald's said no customer data was hacked in the U.S. breach, and the employee data that was exposed was not personal. In a letter to employees, McDonald's warned them to beware of phishing emails and to be careful when asked for personal or business information online.

"While we were able to close off access quickly after identification, our investigation has determined that a small number of files were accessed, some of which contained personal data," McDonald's said, according to CNBC.

McDonald's said while customer payment information was not exposed, it would still notify customers listed in its files as well as regulators.

The company said its South Korea and Taiwan divisions notified regulators in Asia of the breach Friday and that it would contact customers and employees as well.

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