"Foreign interference in the elections has begun,” Tusk wrote on X, adding that investigators had identified "an Eastern trace."
His chief of staff, Jan Grabiec, told public broadcaster Polish Radio that the attack attempted to take control of the party's campaign headquarters' computers and accounting systems handling campaign expenses.
Security services are investigating the case, with preliminary findings indicating the attack originated "from the East," Grabiec said.
The state-owned NASK research institute is also probing the incident, he added.
Digital Affairs Minister Krzysztof Gawkowski said on X that "state services are working intensively" to address the cybersecurity breach affecting the governing Civic Platform (PO) party, led by Tusk.
He described the attack as a "serious matter" and pledged to provide updates as the investigation progresses.
Gawkowski has previously said that Poland "is in a state of cyber Cold War with Russia."
Poles will head to the ballot box on May 18 to elect a new president.
(gs)
Source: IAR, PAP