A report commissioned by the UK government has found that the average cost of cyber security breaches to British businesses has doubled in the past 12 months.
Though the number of companies hit by information security breaches was down on the previous 12 months, the PriceWaterhouseCoopers survey found that the severity and impact of attacks has increased.
The average cost of the worst cyber security breach for big companies was between £600,000 (A$1.1 million) and £1.2 million, up from £450,000- £850,000 in the 2013 survey.
Cyber attacks on companies in Europe and the United States have increased in regularity and severity in recent years as "hacktivists" and criminals become increasingly sophisticated, requiring businesses to strengthen their defences.
In spite of this, the survey found that 81 percent of big companies suffered a security breach in the past 12 months, down from 86 percent in the 2013 study. It also found most companies had increased their spending on IT security.
The audit follows an attack on the Royal Bank of Scotland in December that caused problems for customers accessing their accounts.
British Business Secretary Vince Cable this year said that cyber security is "a top-tier national security priority" and key industries, including finance, energy and transport, have been told to improve plans to protect against disruption to essential services.