After news broke of a major data breach at the world’s largest hotel chain, John Shier, senior security advisor at cybersecurity firm Sophos has some important tips for the millions of guests who may have been compromised.

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 US, 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.