Polish investigators said they found evidence showing a spyware manufacturer harvested data from Polish opposition leaders and other victims and transmitted it to Israel.

Prime Minister Donald Tusk, who ordered the investigation, on Monday called the sprawling spyware operation spearheaded by the country’s previous ruling party “one of the biggest scandals in Polish history since the fall of communism.” He accused Israel-based NSO Group, the spyware manufacturer involved in the scandal, of collaborating with Israeli intelligence services.