Marriott International Inc.’s disclosure last fall that it had inherited a massive data breach when it merged with Starwood Hotels & Resorts Worldwide in a $13.6 billion deal should’ve been a wake-up call from the front desk of cybersecurity and due diligence.  

But only for those who hit the snooze button as Verizon Communications Inc.’s merger with Yahoo Inc. was thrown into jeopardy in late 2016, when Yahoo revealed that about 500 million of its customer email accounts had been hacked.