Three out of four UK businesses at the Airmic conference admitted to having no ecommerce cover to protect against the damage caused by hackers and viruses, finds Lloyd's.
The survey also shows that half the businesses surveyed have been affected by computer viruses and 12% have experienced problems with hacking of their information technology systems.
In addition to asking if businesses had dedicated cyber insurance, Lloyd's also asked businesses to identify the costs of the delays caused by viruses and hacker attacks.
Of those affected by problems, one-in-ten respondents estimated damage to be in the range of £100,000 to £500,000, while the majority, 25%, said the bill was up to £100,000
Max Taylor said: "This survey paints a very worrying picture of unprotected businesses beginning to counter the cost of cyber vandalism.
"What is even more alarming is that without proper ecommerce insurance cover, those costs are going to keep mounting unless there are substantial improvements to IT security in UK organisations.
"Last month, the Love Bug virus was responsible for billions of pounds of damage worldwide and massive business interruption.
"I don't believe there can be any doubt that this is going to be repeated again and again until organisations learn the lessons: tighter security, closer relationships between IT professionals and risk managers, and the recognition that dedicated cyber insurance is vital if revenues and costs are to be protected."
Businesses also admitted to a fear of the ecommerce unknown when surveyed, with respondents identifying exposure to unanticipated liabilities as their major concern.
Last month, a survey by Lloyd's in the US identified ecommerce as the greatest single business risk for the 21st century. Availability of internet liability protection has gone from virtually nothing two years ago to sufficient global insurance capacity to provide cover for risks of up to £200m.