Unrecognizable traveler checks in at the airport by using a self serve kiosk. asiseeit | E+ | Getty Images

A compromised passport number could be your ticket to identity theft woes. Marriott International announced Friday that hackers had accessed the reservation database for its Starwood Hotels brand, compromising data for 500 million guests. For 327 million of those affected consumers, the hotelier said, the information compromised "includes some combination of" data points including name, mailing address, phone number, email address, passport number and date of birth. Some of those guests may also have had their payment card information compromised. "For the remaining guests [in that 500 million total], the information was limited to name and sometimes other data such as mailing address, email address or other information," they said. Experts say the potential for stolen passport numbers makes it more important for affected travelers to keep an eye on their accounts and take steps to protect themselves. (See tips below.)

To replicate a passport takes a lot of effort. I wouldn't necessarily consider your passport compromised. David Kennedy chief executive of TrustedSec

While plenty of individuals deal with a lost or stolen physical copy of their passport, it's less common to see passport numbers included in a breach. "Passports compromised on a massive scale is somewhat unusual," said Eva Velasquez, chief executive and president of the Identity Theft Resource Center. But not unheard of. In August, Air Canada announced its app suffered a breach affecting about 20,000 users, and warned that passport numbers and other details may have been among the accessed data if users had provided them. Equifax said earlier this year that 3,200 passport images were stolen last year as part of its 2017 breach affecting some 148 million consumers.