The Czech Statistics Office says the web sites it used to publish results from a parliamentary election were hacked.
The office made the announcement on Sunday, a day after two sites the office used to post returns of the election for the lower house of Parliament were unavailable for some period of time.
The office described the problem as "massive and sophisticated" attacks that were stopped. It says vote tallying was unaffected.
Police and a Czech government office that deals with cybersecurity are investigating.
The centrist ANO (YES) movement led by euroskeptic populist billionaire Andrej Babis won a landslide victory in Saturday's election, paving the way for Babis to become prime minister.