The International Criminal Court (ICC) said on Friday that the serious cybersecurity incident it detected in September was an act of espionage.

In a statement on the Court’s website, it said the attack can be “interpreted as a serious attempt to undermine the Court’s mandate.”

The statement did not suggest a perpetrator, but the Court — which is based in The Hague in the Netherlands — said that Dutch law enforcement authorities are conducting a criminal investigation.

It is not clear what information, if any, was stolen during the incident. As part of its duties, the Court processes sensitive information relating to war crimes investigations, including data about witnesses who could be at risk if their identities were exposed.

“Should evidence be found that specific data entrusted to the Court has been compromised, those affected would be contacted immediately and directly by the Court,” the ICC stated.

As a result of the attack, the ICC said it was “identifying actions and procedures to be ready to respond to any potential repercussions from the cyber-attack including any potential security risk to victims and witnesses, Court officials and the Court’s operations.”

It noted that the attack comes at a time of “broader and heightened security concerns for the Court,” including threats against several of its elected officials.

Following the Court’s decision to issue arrest warrants for Russian president Vladimir Putin, as well as the Russian Commissioner for Children’s Rights Maria Lvova-Belova for the deportation of Ukrainian children to Russia, Russian authorities in turn issued arrest warrants against the ICC president, deputy, and one of its judges.

In June 2022, Dutch intelligence detained an alleged Russian military intelligence officer using an elaborate false Brazilian identity in an attempt to infiltrate the ICC. The man has since been deported back to Brazil, where he is being prosecuted for using false documents.