Businesses experienced an average of one hacking attempt per week, four per cent of which had their systems penetrated, according to research from the Department of Trade and Industry.
"[It] points to a real concern that businesses without the right monitoring and intrusion prevention processes in place may have a false level of comfort," said Andrew Beard, who was involved in the survey with PricewaterhouseCoopers. "Scanning and hacking activity may not be detected until it is too late to react."
Seventy-two per cent of firms surveyed expressed confidence in their ability to detect or prevent security breaches.
However, three-quarters of companies that experienced penetration rated it as the worst security incident of the year.
Firms saw firewalls as the main line of defence against intrusion, although in 50 per cent of cases, this was their only defence.
"Proactive prevention technologies to combat both internal and external attacks are a commercial necessity," said Sarah Whipp, senior director of marketing at McAfee Security.