Security firm Webroot recorded a dramatic rise in spyware in the past 12 months, almost all of it aimed at harvesting financial data that could be used by third parties.
Experts have also warned that the next target for such malware will be VoIP applications such as Skype.
"Voice is definitely the next attack vector. But this time the malware writers won't use it for financial gain but for stealing intellectual property, " said Gerhard Eschelbeck, chief technology officer at Webroot.
Eschelbeck claims to have identified significant changes in the way spyware is being developed compared to viruses.
Viruses tend to be developed and distributed by individuals before being used by third parties. Spyware, on the other hand, is typically developed by teams working to order and learns the lessons of viruses.
Some code even resets sections of itself every hour in an effort to fool signature-based security software.
'Build your own spyware' kits are already commonplace on the internet in publicly available forums, leading to fears that 'script kiddies', technically unsophisticated users, could develop and distribute their own malware.
Eschelbeck added that his company had seen a 40 per cent rise in the amount of spyware in circulation over the past three months, and warned that the availability of spyware kits will fuel further rises.
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