Businesses are facing a growing threat from worms and Trojans designed to steal confidential information from corporate systems.
Over the past six months, the proportion of malicious code targeting confidential information has grown from 50% to 74% of all attacks, Symantec's latest internet security threat report reveals.
The escalation comes amid growing evidence that hackers are developing malicious code or renting out networks of infected computers for financial gain.
Organisations have faced an onslaught of attacks from worms with the capability to provide hackers with back door access to data on their corporate systems.
They include worms such as the Mytob family, which appeared in 97 variations in June, as hackers attempted to keep one step ahead of anti-virus systems.
Earlier this year, an international police investigation revealed that private detectives had used a custom-made trojan to steal business plans and other confidential information from leading Israeli businesses.
Last year police were called in after criminals planted key loggers on the computer systems of Sumitomo Bank in the City of London, during an attempt at an electronic bank heist.
Criminals are increasingly resorting to using phishing e-mails, which attempt to obtain confidential passwords and user names from online banking websites, Symantec reveals.
Over the past six months the number of phishing e-mail attacks has grown from 2.99 million a day to 5.70 million a day, equivalent to one in every 250 e-mails.
In another attack to appear this year, criminals infect systems with a Trojan, which encrypts documents, spreadsheets and database files. Users then have to pay £110 to buy software to decrypt the files.
Evidence has emerged that hackers are hiring out networks of infected computers, known as bots, to criminals to use for mass mailing spam, or launching denial of service attacks. The Symantec research suggests that criminals rent out bots for as little as £160 for a network of 150,000.
Over the last six months, the UK had the highest proportion of bot-infected computers worldwide at 32%, reflecting the nation's high take-up of broadband. The US was second, with 19%.