Marriott International Inc. is the latest major corporation to suffer a massive data breach and exposing customers to potential hacking dangers. According to a report from Reuters, it was the hotel company’s booking database system for its Starwood line of properties. The data breach may have exposed financial information of more than 300 million customers. It wasn’t just financial data that was potentially stolen either; hackers may have accessed customer’s “passport details, birthdates, addresses, phone numbers, and email addresses.”

“What makes this serious is the number of people involved, the intimacy of the data that was taken and the long delay between the breach and discovery,” said former US attorney specializing in cyber crimes Mark Rasch while speaking to Reuters.

While breaches like this one are becoming more common, the Starwood incident may wind up doing far more damage as the attack went on for so long. CNBC reports that the attack began in 2014, meaning hackers may have potentially been stealing data for the last four years. Due to the cataclysmic size of the breach, a class action suit against the hotel juggernaut has already been filed in Maryland.

“Large, sophisticated companies like Marriott are not blind to the risks posed by cyber criminals, who are constantly attempting to infiltrate corporations that store sensitive consumer information,” wrote attorney John Yanchunis of Morgan & Morgan, the firm initiating the suit in a statement to Gizmodo. “The fact that a breach that began in 2014 went undetected for four years is shocking and horrifying. When guests stay at hotels, they trust the hotel will provide adequate security — both physical and the protection of their private information. It appears that the trust 500 million people placed in Marriott/Starwood was violated — for nearly half a decade.”

In the wake of the announcement, shares of Marriott dropped by more than five percent and is currently trading at $115.03 at the time of this writing. However, not everyone is convinced this incident will have long-term impacts on the company’s earnings. A report from MSN, Equifax, which suffered a similar massive information breach initially saw its stock price plummet after the news broke, but the company quickly regained its footing. With the holiday season in full swing, Marriott may be able to shake the incident off without too much damage.

The Federal Bureau of Investigation is already investigating the case, and Gizmodo reports that the hotel company is “cooperating with law enforcement.”

“We fell short of what our guests deserve,” Marriott said in a statement. According to Reuters, the company has known about the breach since the beginning of September. It is unknown what prompted the company to announce the breach at this time.