Some of the world’s biggest insurers plan to work together on an assessment of the best cybersecurity available to businesses, an unusual collaboration that highlights the rising dangers posed by digital hackers.

The program, which was launched Tuesday by the Marsh brokerage unit of Marsh & McLennan Cos., will evaluate cybersecurity software and technology sold to businesses. Marsh will collate scores from participating insurers, which will individually size up the offerings, and identify the products and services considered…