Hackers exploited a loophole on Pinduoduo ’s platform, stealing vouchers worth tens of millions of yuan on Sunday morning.

The group-buying platform has fixed the system bug and is tracking the source of the purchases. The company has reported the case to the police, according to a statement on its official Weibo account.

Pinduoduo was formed in 2015. The fast growing e-commerce platform allows consumers to group together to increase the discounts offered by merchants. The company filed for an initial public offering (IPO) on Nasdaq last July and is now valued at 27 billion U.S. dollars.