Bots accounted for 35 percent of all malicious code detected in April, an increase of 14 percent from March figures, according to security vendor Fortinet.
Trojans still accounted for the majority of malicious code detected, accounting for 39 percent during April. However, this had declined by 20 percent from figures reported in March.
The figures are indicative of the increasing motivation of financial gain amongst virus writers. As internet users become more security aware, virus writers are being forced to deploy new techniques to facilitate the mass propagation of their code, the company said in a statement.
Guillaume Lovet, team leader of the EMEA threat response team at Fortinet, said that computer users were adhering to the advice of antivirus vendors.
"Given the number of virus outbreaks over recent times, it is highly likely that regular users of the internet have been infected at least once in their life -- and having learnt from their experience are naturally more cautious about opening attached files," he said.
The increased awareness has caused malware authors to develop code designed to propagate without user intervention, the company said.
"The most impressive technique we saw this month was the large scale pharming attacks that targeted key DNS servers -- this meant that all users depending on these servers had their requests for any .com address redirected to a malicious site; this site was serving web pages infected with typical browser exploits, in turn installing adware/spyware on the unfortunate user's computer," Lovet said.