Holiday booking firm TripAdvisor has warned customers that their email addresses may have fallen into the hands of spammers.
The investigation is ongoing as to how the email details were compromised, and how many customers had been affected, a company spokeswoman told ZDNet UK on Thursday.
TripAdvisor co-founder Steve Kaufer said in a letter to customers on Thursday: "This past weekend we discovered that an unauthorised third party had stolen part of TripAdvisor's member email list. We've confirmed the source of the vulnerability and shut it down. We're taking this incident very seriously and are actively pursuing the matter with law enforcement... You may receive some unsolicited emails (spam) as a result of this incident."
Customer password information is secure, and TripAdvisor does not collect credit card details, the company said in an explanatory note on its website.