The cost of cyber insurance is heading higher just as more companies are deciding to buy the coverage.

A recent outlook from insurance brokerage Willis sees premiums for most types of commercial insurance declining in 2016. But in the wake of a string of breaches in which hackers exposed mountains of data at big companies, Willis said cyber premiums could rise as much as 15% next year. Companies that are seen as particularly vulnerable to breaches, such as retailers and health care providers, could see price hikes of up to 150%, Willis said, but noted that small companies should see smaller increases.

"With some of the recent mega breaches, with some of the limit losses out there, the underwriters had to adjust their pricing," said Neeraj Sahni, vice president for cyber and technology risks at Willis' FINEX North America division.