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(CNN Business) —  

If you’ve stayed at a Starwood hotel in recent years, there’s a good chance you’ve been impacted by a massive data breach that potentially exposed the personal data of about 500 million guests.

Marriott — which owns Starwood hotels such as the St. Regis and the Westin — on Friday disclosed that the Starwood guest reservation system had been hacked, in a breach dating back to 2014.

For 327 million people, Marriott says, the exposed information includes names, phone numbers, email addresses, passport numbers and dates of birth. For millions of others, credit card numbers and card expiration dates were potentially compromised. This kind of information could be used to steal your identity and open bank accounts, credit cards or loans in your name.

It’s the second biggest corporate data breach in history, behind one involving Yahoo, which said last year that 3 billion accounts among several of its brands were compromised.

Marriott said it will start emailing users who were impacted and it has set up a website with information about the breach.

In the meantime, here’s what you can do to protect yourself:

Change your password

Marriott says guests should change their passwords regularly and pick ones that aren’t easily guessed. For example, instead of a common phrase, choose a combination of four or more unrelated words with numbers, characters and a mix of upper and lower-case letters.

You should also have different passwords for all the services you use.

“Changing your password will just add one more roadblock to a potential hacker getting into your system,” said Aaron Brantly, a cybersecurity expert at Virginia Tech.

Many websites, including social media and financial accounts, offer two-factor authentication for an added layer of security. Even if someone obtains your password, you can’t access your accounts without a second piece of information, like a code texted to your phone.

Monitor your accounts for suspicious activity

Marriott recommends customers keep an eye on their Starwood Preferred Guest account for any suspicious activity. Guests should also check their bank, retirement, and brokerage accounts, as well as credit card statements to look for any unauthorized transactions.

Some experts recommend signing up for credit monitoring services or identity theft protection. A more extreme step is putting a freeze on your credit, which blocks anyone from accessing your credit reports without permission.

“Unfortunately, the reality is [these consumers] have to monitor continuously, for generally the rest of their lives,” said Brantly. “These types of accounts are sold regularly on the dark web. … You can usually buy credit card information for a couple dollars per credit card online.”

Vivek Lakshman, VP of innovation at cybersecurity firm ThumbSignIn, says consumers can also enroll in services like WebWatcher – which Marriott is providing for free for a year – to track their exposure. These sites monitor websites where personal information is shared and alerts consumers if there’s evidence of their information exposed online.

Open a separate credit card for online transactions

Yair Levy, a cybersecurity and information systems expert at Nova Southeastern University, recommends having a credit card dedicated to online shopping. This makes it easier to track transactions and spot fraudulent activity.

If that credit card is compromised, you also won’t have to update automatic payments for things like bills.

Limit the information you share

Exper