TripAdvisor advertises itself as the â€œmost trustedâ€ site but has recently fallen victim to hackers.
An email sent to members from the website's CEO Steve Kaufer said hackers had managed to get hold of a "proportion" of its members list.
He reassured them that the source of the "vulnerability" had been found and shut off.
All member passwords are secure, said Kaufer.
SC Magazine, a publication for security professionals, said TripAdvisor had told members it was taking the incident very seriously and had contacted law enforcement officials.
The incident was discovered over the weekend of March 19.
The review website did not reveal how many of its users were affected.
TripAdvisor's website says it has 20 million members.
By David Wilkening, TravelMole USA
Thursday, March 31, 2011