A rash of hacking attacks on U.S. companies over the past two years has prompted insurers to massively increase cyber premiums for some companies, leaving firms that are perceived to be a high risk scrambling for cover.

On top of rate hikes, insurers are raising deductibles and in some cases limiting the amount of coverage to $100 million, leaving many potentially exposed to big losses from hacks that can cost more than twice that.

"Some companies are struggling to find the money to buy the coverage they want," said Tom Reagan, a cyber insurance executive with Marsh & McLennan Co's (MMC.N) Marsh broker unit.