The Norwegian Police Security Service suspects pro-Russian hackers sabotaged a dam in southwestern Norway in April.

Norwegian daily newspaper VG reported that the hackers breached the dam’s control system, opening valves for four hours, sending large amounts of water gushing forth until the valves could be shut.

The chief of the Norwegian Police Security Service (PST) Beate Gangås, disclosed the incident during a presentation on pro-Russian cyber operations at a public event on Wednesday.

According to VG, Gangås said that the number of cyberattacks on Western infrastructure was increasing, often not to cause damage but to “demonstrate what they are capable of.” She also said Norway should be prepared for further hacking attacks.

At the same event, Nils Andreas Stensønes, head of the Norwegian Intelligence Service said that Russia was the biggest threat to Norway’s security.

Cyberattacks on Western targets are part of Russia’s hybrid warfare strategy. In another water-related case in January 2024, a hacking group breached a Texas water facility’s system, causing it to overflow. The suspected hackers are linked to the Kremlin.

The dam is located in the municipality of Bremanger, approximately 150 kilometers north of the city of Bergen. Local media say that the dam is not used for energy production and that the hackers might have exploited a security gap created by a weak password.