Google GOOG, -2.37% GOOGL, -2.41% said on Wednesday that it is requiring almost 100,000 users to change their passwords after their credentials were found on a Russian bitcoin forum.

Reports began circulating Wednesday that about 4.93 million Google usernames and passwords had been dumped onto a Russian-language bitcoin security forum, less than 2% of which might have worked. The company says its systems weren't breached and the credentials likely came from other compromises involving users who recycle passwords for multiple accounts, or malware or phishing attacks.