A massive 500-million people have been compromised in one of the world’s biggest data breaches to date.

Marriott has confirmed a data security incident involving the Starwood guest reservation database, with investigations determining that there was unauthorised access to the database, which contained guest information relating to reservations at Starwood properties.

On 8 September 2018, Marriott received an alert from an internal security tool regarding an attempt to access the Starwood guest reservation database in the US. The company engaged leading security experts to help determine what occurred.

Marriott learned during the investigation that there had been unauthorised access to the Starwood network since 2014. It discovered that an unauthorised party had copied and encrypted information, and took steps towards removing it. On 19 November 2018, Marriott was able to decrypt the information and determined that the contents were from the Starwood guest reservation database.

The company has not finished identifying duplicate information in the database, but believes it contains information on up to approximately 500-million guests who made a reservation at a Starwood property.

For approximately 327-million of these guests, the information includes some combination of name, mailing address, phone number, email address, passport number, Starwood Preferred Guest account information, date of birth, gender, arrival and departure information, reservation date, and communication preferences.

For some, the information also includes payment card numbers and payment card expiration dates, but the payment card numbers were encrypted using Advanced Encryption Standard encryption (AES-128). There are two components needed to decrypt the payment card numbers, and at this point, Marriott has not been able to rule out the possibility that both were taken.

For the remaining guests, the information was limited to name and sometimes other data such as mailing address, email address, or other information.

Marriott reported this incident to law enforcement and continues to support the investigation. The company has already begun notifying regulatory authorities.

“We deeply regret this incident happened,” said Arne Sorenson, Marriott’s president and CEO. “We fell short of what our guests deserve and what we expect of ourselves. We are doing everything we can to support our guests, and using lessons learned to be better moving forward.”

In a big to mitigate damage to customers, Marriott is providing guests the opportunity to enroll in WebWatcher free of charge for one year.

WebWatcher monitors internet sites where personal information is shared and generates an alert to the consumer if evidence of the consumer’s personal information is found.

John Shier, senior security advisor at Sophos, comments: “The potential fallout from the Marriott’s Starwood data breach should be alarming to anyone who has stayed at a Starwood property in the last four years. Not only are guests at risk for opportunistic phishing attacks, but targeted phishing emails are almost certain, as well as phone scams and potential financial fraud.

“Unlike previous breaches, this attack also included passport numbers for some individuals who are now at increased risk for identity theft. At this point, however, it’s unclear what level of exposure each individual victim has been subject to. Until then, all potential victims should assume the worst and take all necessary precautions to protect themselves from all manner of scams.”

Sophos recommends these tips:

* Be on alert for spearphishing: Marriott has said that personal details associated with the Starwood Preferred Guests accounts have been compromised, and personal email addresses are vulnerable. This creates the perfect scenario for cybercriminals to actually spearphish consumers because they have this type of detailed information.

* Be on alert for opportunistic phishing: Marriott has said it will email Starwood Preferred Guests those who may be impacted. Do not click on links in emails or other communication that seem to have come from Marriott or Starwood hotels. It’s possible that criminals will try to take advantage of this by sending malicious tweets or phishing emails that look like they’ve come from the company. Hover over URLs and links to see the address before you click. Look at the email address to see where it is from.

* Monitor your financial accounts: Reports indicate the attackers may have access to some members’ encrypted credit card information, but it’s not clear as of yet if this information can be decrypted; in general, monitor your credit card for suspicious activity. As a safety precaution, change the password to your online credit card account. If you use the same password for similar financial management websites, immediately change the password on those websites. As a best security practice, always choose a different, strong password for each sensitive account.

* Change passwords, as a precaution: It’s not clear as of yet if the attackers have access to Starwood Preferred Guest account passwords, but as a safety precaution, consumers can change their password. If this password is also used for any financial accounts, change those immediately. Monitor your Starwood Preferred Guest account for suspicious activity.

* Don’t Google “Web Watcher”: Marriott is offering victims in the USA, UK and Canada a free, one year subscription to something it calls WebWatcher, which it describes as a service that monitors “internet sites where personal information is shared.” Don’t Google it. If you Google “WebWatcher” you won’t find the monitoring service, you’ll find lots of links to spyware of the same name. Don’t sign up for that. Do follow the links to country-specific versions of the official breach site. You cannot sign up for monitoring from the main breach page, you have to go to the all-but-identical versions of the page for the US, UK or Canada