According to a report from BitDefender, malware which spreads by abusing the Windows AutoRun feature was the most prominent threat on the Internet during the first half of 2010. China and Russia topped the list of countries that host malicious programs.

AutoRun is a Windows feature long abused by malware authors to spread their malicious creations. In fact, the risks posed by this functionality outweigh the benefits so much that many sec urity experts and antivirus vendors recommend disabling it altogether.

There is also an increased prevalence of PDF exploits with the generic Exploit.PDF-JS.Gen signature being the third most triggered one this year. The malware distributed through these PDF attacks is obviously also common.

As far as malware origin is concerned, China was responsible for hosting 31% of it. Russia is also responsible for harboring many of the world malware distribution operations, with 22% of the world's malware being hosted in this country. Brazil came next with a rate of 8.10%, the researchers noting that banking trojans are particularly prevalent here. The United States, a prominent malware-hosting country in the past, only ranked fifth this year with 5,0% and after UK with 6,00%. Spain (4,16%), Germany (3.80%), Sweden (2.91%), France (2.30%) and Ukraine (3.46%) complete the top 10.

Ref: http://news.softpedia.com/news/AutoRun-Malware-Dominates-the-Threat-Landscape-in-2010-147715.shtml