An unidentified hacking group has gained access to the internal IT network of the 2021 National Games of China.

The competition, which took place in September 2021 in the city of Shaanxi, is an internal sporting event for Chinese athletes only, modeled after the rules of the Olympic Games and the event where national champions are crowned across different sporting events.

Avast said that roughly 12 days before the event’s start, unknown attackers gained access to a public server and an SQL database belonging to the event’s organizers and proceeded to install web shells so they could access systems at later points.

“After gaining access, the attackers tried to move through the network using exploits and bruteforcing services in an automated way,” Avast said in a report published on Thursday.

To achieve lateral movement, Avast said the attackers used an exploitation framework written in the Go programming language that included plugins for several known vulnerabilities.

The security firm said it learned of the incident from an incident response report that contained details about the breach its researchers found on VirusTotal, a web platform owned by Google where users can upload and scan files for malware.

“Based on the initial information from the report and our own findings, it appears the breach was successfully resolved prior to the start of the games,” Avast added.

The Czech security firm said it was unable to determine what information the hackers stole but said that they “have reason to believe [the attackers] are either native Chinese-language speakers or show high fluency in Chinese.”