Trojans make up nearly three quarters of all new malware detected between April and June this year, says Panda Security.
According to the security firm's PandaLabs division, quarter two of 2009 also saw a six percent drop in spyware, which now accounts for just seven percent of all new malware.
Adware, however, has risen, and in Q2 made up 16.37 percent of all malware detected. PandaLabs says the increase is due to fake antivirus applications - a type of adware that passes itself off as a legitimate security solution.
Trojans were also responsible for more infections. The security firm identified 34 percent of infections between April and June this year were Trojans, and Downloader.MDW was the Trojan that caused the most infections.
In terms of specific strains of malware, the number one ranked specimen between April and June 2009 was, a Trojan designed to download other malware on to computers.
The security firm also revealed that Twitter worms, that use a cross-site scripting technique to infect other users of the micro-blogging service when they visit an infected page, were on the up.