Investigators say Russian hackers are responsible for the attempted blackout in Poland

A failed attempt in December to bring down parts of Poland’s power grid was the work of Russian hackers known for causing power outages in the past, according to a security research firm that investigated the incident.

Last week, Polish Minister of Energy Milosz Motyka he told reporters that an attempted cyberattack on December 29 and 30 saw hackers targeting two thermal and power plants, as well as attempting to disrupt communications between renewable installations, such as wind turbines and power distributors.

Motyka called the incident “the most powerful threat” to Polish energy in years, by the Polish government to blame Moscow for testing. Local media report that an attack could knock out heat and power to at least half a million homes across the country.

On Friday, the cybersecurity company ESET it said it received it copy of the malware, which it calls DynoWiper. This type of malware, known as “wiper” malware, is designed to simply destroy data on computers so they don’t work.

ESET said the malware is “medium trust” and a known hacker group Sandworma group within the Russian military’s GRU, based on “significant connections” with its previous investigation of the Sandworm malware, including the group’s use of the malware against Ukrainian forces.

Freelance reporter Kim Zetter first report story.

According to Zetter, the cyberattacks targeting Poland come almost a decade after Sandworm launched the first cyberattack on Ukraine in 2015, causing power outages in more than 230,000 homes around Kyiv, the country’s capital. A similar cyberattack occurred in Ukraine a year later.

After the hacking attempt, Poland’s prime minister, Donald Tusk, said that the country’s cyber security had worked, and “there was no harm done.”