Marriott’s massive data breach exposed more than just 500 million customer records, it is also shining a light on the role cybersecurity needs to play when a firm is in acquisition mode, along with the damage that even one slip up by an employee can have on the entire company.

Marriott has not disclosed exactly how cybercriminals managed to enter the Starwood reservation system compromising 500 million records, but the early action on the breach is leaning toward the malicious actors obtaining employee credentials in some manner and gaining access to the system. And since their presence was in place two years before Marriott’s purchase of Starwood Hotels there was an obvious omission by Marriott during its vetting process of Starwood and its computer network.

The general consensus is the breach did not involve a hack using malware, but a few other possibilities have been broached. Ben Johnson, co-founder and CTO of Obsidian Security, thinks the attacker originally gained entry through an employee error.

“Often threat actors obtain employee-level access and ‘live off the land’, using built-in tools and IT systems to traverse the environment. Furthermore, due to a lot of the reporting being around encrypted data, it’s highly possible that it was a database backup system that was compromised, as the backup systems often have lower security scrutiny than production,” he told SC Media.

Phishing has also popped up as one possible path of attack.

“At this point, we can only speculate, but if I had to guess, phishing would be at the top of the list. My second guess would be a third-party vendor compromise – possibly via phishing or other poor security practices like an unpatched vulnerability – that gave them a foothold within the Starwood enterprise,” said David Pearson, principal threat researcher at Awake Security.

Sherban Naum, senior vice president for corporate strategy and technology at Bromium, added that once the malicious actor was ensconced in Marriott’s system, however the method, he really went to work.

“Often, hackers will gain a foothold through an unsuspecting user and spend time working their way through the network, escalating privileges in order to access a company’s crown jewels. The longer a hacker has access, the more damage they can do, so this is much more serious than a one-off breach, continuously putting customers at risk of targeted phishing attacks and card fraud,” he said.

Another point brought up by Marriott in its breach statement is despite having encrypted customer payment card data it cannot assure those affected that the criminals did not take the keys and access the information. This fact stood out to Michael Daly, CTO, cybersecurity and special missions at Raytheon Intelligence, Information & Services.

“From a technical standpoint, what stood out to me is they appear to have lost the private decryption keys. This demonstrates again that encryption itself won’t secure data in today’s environment. Active monitoring, proactive threat hunting, automation and an overall holistic approach are required for data security,” he said.

What exactly happened to the data is also not known at this point, but Michael Thelander, Venafi’s director of product marketing, said the true details may not come out until the stolen data is used.

“Session logging might tell where SSH keys were used while the attackers were in the network, but there’s a real possibility that keys could have been exfiltrated in parallel with the data. If that’s the case, we may not know it happened until newly-decrypted payment card data begins to drive new fraud schemes,” he said.

Some of the attacks that could ensue from the stolen data are opportunistic and targeted phishing emails, as well as, phone scams and potential financial fraud, said John Shier, senior security advisor for Sophos.

“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,” Shier added.

And if money was not the driving reason behind the attack Raytheon’s Daly suggested the attack could be politically motivated.

“This is much more than a consumer data breach. When you think of this from an intelligence gathering standpoint it is illuminating the patterns of life of global political and business leaders including who they traveled with when and where. That is incredibly efficient reconnaissance gathering and elevates this breach to a national security problem,” he said.

Another fact this data breach highlighted is the need for, and the difficulty of, doing a proper job vetting a company’s computer system prior to finalizing an acquisition.

Marriott closed on Starwood Hotels in 2016, but the company’s internal security team has already determined that unauthorized access to its database had existed from 2014. However, the cybersecurity risk involved to the buyer whenever a corporate takeover happens requires greater attention and time be spent examining every digital nook and cranny of the acquisitions network.

“Cybersecurity is and should be a critical due diligence component for any acquisition. This includes pen testing, code reviews, SOC reviews and other exams to test internal controls around the security and confidentiality of the target’s assets,” said Darren Guccione, CEO and co-founder of Keeper Security.

Shape Security Director of Engineering Jarrod Overson pointed out the difficulty involved in vetting another company primarily the landscape could simply be too big to properly cover.

“This breach highlights the risk of acquiring companies and attempting to integrate disparate technical systems. Marriott may have the best security in the world but absorbing an entire company’s worth of services, servers, and applications opens up a lot of opportunity for incidents and monitoring to fall through the cracks,” he said.

Then there is the problem of balance. During any acquisition, there is a need to move the process along as expeditiously as possible, while attempting to be thorough and limit costs. A very difficult trick to pull off.

“Conducting comprehensive security audits takes time, and can slow down the acquisition process. Ultimately, the goal has to be a balance of assurance and economic benefit. Acquirers should look for demonstrable security best practices,” said Tim Erlin, Tripwire’s vice president of product management and strategy.

Erlin added the company being acquired also needs to prove its cybersecurity house is in order, a fact that could also boost the value of a company to any prospective buyer. If for no other reason than to give an interested party the peace of mind that an acquisition will not result in damage to the buyer’s system.

“There’s a risk that this attack may have spread from Starwood systems into Marriott’s systems,” said Matt Aldridge, senior solutions architect at Webroot.