A survey of 100 IT decision makers found that 85% of organisations using traditional security systems for their physical and virtual environment are leaving themselves open to threats.
The survey by security specialists Trend Micro and Vanson Bourne also found that 66% of organisations experienced security breaches in recent months, with only half picked up by traditional security methods.
Trend Micro’s technical director Michael Darlington, said: "Virtualisation security is still being viewed as an afterthought as businesses ‘make do’ with the same security policies, process and tools they would use in a physical environment.
"This approach is leaving organisations open to the risk of cyber-attack as they fail to realise that a new security mind-set is required."
Asked about their virtualised environments, 92% of organisations said they struggled to keep it secure, while 93% said that it had complicated their IT systems. And 39% said using Infrastructure-as-a-Service (IaaS) had made managing security more complex.
"IT transformation is at its most impactful when security and virtualisation experts work together to create a solution that reduces cost and improves productivity whilst managing risk," said Darlington.
"By adopting a new mind-set and recognising the security posture needs to change in line with IT environments, British businesses will be well placed to realise the benefits of virtualisation without compromising on security," he added.
The figures come as the UK government starts a £4m information security awareness campaign, as part of its efforts to make businesses aware of the threat posed by online crime.