Google's web-based e-mail system, Gmail, has been targeted as part of an "industry-wide phishing scheme".
The firm said that it had immediately safeguarded the affected accounts. BBC News has seen two lists that detail more than 30,000 names and passwords from e-mail providers, including Yahoo and AOL, which were posted online.
The lists also include details of thousands of Microsoft Hotmail users. Google said fewer than 500 of its accounts had been affected by the scam. more