Millions of Gmail users are thought to have been targeted in a major phishing attack spread via emails from genuine friends and acquaintances.
Large numbers of people reported they had been hacked after receiving an email from a known contact asking them to open a link to what appeared to be a Google document page.
Many of those who clicked through unwittingly allowed hackers to take control of their accounts, including giving access to their email and address books and allowing the scam to be spread onwards.
Gmail said that it had taken action to remove the faked pages and had added extra security features to stop the hackers after it was made aware of the major phishing attack.
Security experts reported that those targeted had been asked to click a link and were then prompted to give permissions to an app claiming to be Google Documents but which was in fact a faked page.
Anyone who was taken in allowed the scammers access to all of their Google accounts, including Gmail and Google Documents.
In a statement, Google said anyone who received a suspicious email with a link to a Google Document should not open it and should report it as phishing within Gmail.
Those who fear they may have been hacked should go through a security checkup to regain control of their accounts, the company added.