Two-thirds of big UK businesses have been hit by a cyber attack in the past year, according to government research.
Most of the attacks involved viruses, spyware or malware, the Cyber Security Breaches Survey says. A quarter of large firms experiencing a cyber breach did so at least once a month.
Digital Economy Minister Ed Vaizey said it was "absolutely crucial businesses are secure and can protect data".
In some cases the internet-linked attacks cost millions of pounds.
The survey's results have been released alongside the government's Cyber Governance Health Check, launched following the TalkTalk cyber attack in October last year.
The phone and broadband provider, which has over four million UK customers, said some of their banking details and personal information could have been accessed in the breach.
In light of these surveys, businesses are now being urged to protect themselves better.