Security researchers say that hackers infected tens of thousands of computers from the Taiwanese vendor ASUS with malicious software last year through the company’s online automatic update service.

Kaspersky Lab, a Russian cybersecurity firm, said Monday that it detected 57,000 infections among its customers. It estimated that the hack may have affected more than 1 million computers from the world’s No. 5 computer company.

The malware was designed to open a “backdoor” for intruders in the infected machines.

Kaspersky said most of the infected computers detected were in Russia, Germany and France, followed by Italy and the United States.

The attack was first reported by the online news site Motherboard. ASUS did not immediately respond to emailed requests seeking comment.

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