Japanese eyeglass lens maker Hoya Corp. was hit by a cyberattack at its key production base in Thailand in late February, leading to a partial shutdown of its factory lines for three days, company officials said Saturday.

About 100 computers were infected with a virus that steals user IDs and passwords, which the company believes was a precursor to spreading another virus to enable the unauthorized use of its computers for cryptocurrency mining. The company says it prevented the second phase of the attack.

In a process called mining, digital currency is awarded to individuals and groups that leverage their computer processing power to perform complex mathematical calculations necessary to maintain and validate the currency's transaction history.