UK National Lottery operator Camelot has brought in law enforcement after becoming aware that hackers have again illegally accessed players' online accounts.
Around 150 accounts were hacked, although customers have been reassured that no sensitive information such as debit card or bank account details were accessed.
On less than ten affected accounts some limited activity may have taken place, Camelot said, but none that would see players incur financial losses.
All affected accounts have now been suspended, with players contacted directly to help them safely reactivate the service. All of the National Lottery's 10.5m registered online players are also now being advised to change their online passwords as a precaution.
The lottery operator added that there was no unauthorised access to core National Lottery systems or any of Camelot's databases which could affect draws or prize payouts.
"Protecting our players' personal data is of the utmost importance to us," Camelot said. "We are very sorry for any inconvenience this may cause and would encourage those with any concerns to contact us directly, so we can discuss it with them in more detail."
The operator has reported the breach to the police and Information Commissioner's Office and is liaising with the National Cyber Security Centre on the matter.
Camelot faced a similar, though much larger, breach in 2016 when up to 26,500 accounts were illegally accessed by hackers. In that case, it said that email addresses and passwords may have been stolen from another website for which players use the same details, allowing the hackers to access personal information.