Virus researches on Monday said Trojans accounted for 70 percent of all new malware between April and June 2009 and are responsible for over a third of all infections.

Downloader.MDW was the most aggressive strain of malware in April to June, according to Panda Lab Security study. Trojans accounts 34.37 % of all Trojans type of malware.

In terms of specific strains of malware, the number one ranked specimen between April and June 2009 was Downloader.MDW, a Trojan designed to download other malware on to computers. The Virtumonde spyware and Rebooter.J Trojan were also among the malicious codes that caused most infections.

When broken down geographically, Taiwan continues to top the list with 33.63 percent of computers infected with active malware. Turkey and Poland come next, with just under 30 percent.

Three Scandinavian countries, Sweden (14.2 percent), Norway (12.48 percent) and Finland (12.17 percent), are the countries with the lowest number of computers infected by active malware during the first half of 2009.

The malicious use of Twitter also is also up with advances of BlackHat SEO techniques and a in-depth Waledac worm that spread across the site.