Hackers believed to be affiliated with Russia’s military breached the Ukrainian gas company where former Vice President Joe Biden’s son had served on the board as it became a focus of the impeachment inquiry into President Donald Trump, according to a U.S. cybersecurity firm.

Attempts to hack into Burisma Holdings began last November, as Congress was holding hearings into whether Trump abused his office by pressuring his Ukrainian counterpart to work with his personal lawyer, Rudy Giuliani, to investigate Biden and his son, Hunter, according to research published Monday by Area 1, a California-based company.

The hacking attempts are ongoing and are linked to the Russian military intelligence unit previously known as the GRU, which hacked and leaked Democratic emails during the 2016 presidential election, Area 1 said.

It wasn’t known what information the hackers were seeking or what they obtained, the firm said. In at least one instance, the hackers tricked the recipient of a phishing email into sharing login credentials that allowed them access into one of Burisma’s servers, the company said. Area 1’s findings were earlier reported by the New York Times.

An expanded version of this report appears on WSJ.com.

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