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The breaches put corporate computer systems out of action for an average of four hours, with the worst incidents causing up to eight hours of downtime, the survey by research firm Vanson Bourne revealed.
Only 20% of companies said they have complete confidence in the security of their data, with financial companies tending to be the most confident and manufacturing firms the least confident about their systems.
More than 25% of the IT managers questioned said they had refused to grant access to their Web sites to customers, suppliers or partners because of security concerns. The figure rose to 32% in the finance sector and 35% among larger companies.
More than 50% of the firms in the Oracle-commissioned survey said they find it difficult to keep information secure. Smaller companies were most concerned about threats from their own employees, while larger companies tended to see external threats as more of a worry.
Richard Baron, deputy head of policy at the Institute of Directors, said businesses are having to strike a difficult balance. "E-commerce can deliver tremendous benefits through instant sharing of information. But those benefits rely on companies trusting people both inside and outside their firewall," he said.