Officials in Poland say computer hackers have attacked the website of the country's electoral commission, which is still unable to publish full returns from local elections because of an unrelated computer glitch.

The State Electoral Commission says while the website hacking incident didn't add further difficulties to the vote counting process, it ordered its officials to change their passwords Wednesday.

But the problems have undermined the credibility of Sunday's vote, which has been seen as a test of strength for new Prime Minister Ewa Kopacz before next year's general election.

Exit polls suggested a win for the opposition Law and Justice party in provincial assemblies, but the official returns for the assemblies were still unknown Wednesday, after the computer system failed, forcing a count by hand in some places.