USB worms and Trojans were among the top five most prevalent forms of malware in the first quarter this year, and spammers customized their subjects by a victim's country, according to McAfee's newly released threat report.

The No. 1 malware type was an Autorun USB worm called "Generic! Atr," followed by different password-stealing Trojans, including one that targets online gaming, as well as an Autorun Conficker worm.

Spammers used different email subjects depending on the targeted victim's country: Diploma spam was hot in China, South Korea, and Vietnam, while Japan, Hong Kong, and Singapore received a large amount of spam with subject lines related to Delivery Status Notification.

"Most of the major cybercriminals are understanding social engineering better now," says Dave Marcus, director of research and security for McAfee. "Diploma-labeled spam as a lure is very prevalent in one part of the world, but not in another. It doesn't work on American audiences, [for example]."

Marcus says one big theme in the report was more targeted, customized attacks.

"This is validation of what we've been talking about for a while. The [attacks] are solely focused on making money with cybercrime," he says. "Anyone who's been around security for the last year or two shouldn't be surprised that USB worms are one of the top five, followed by a variety of Trojans. "

One change from previous reports is that the popularity of the malware threats was consistent across countries and regions, according to McAfee.

Marcus says spammers and botnet operators are relying more heavily on Twitter and Google trends and terms in their quests to better customize and target their attacks. "They are seeding botnets simply that way. They can go to Google Trends and see what words are trending heavily, and that's what's fed into the spam run," he says. "They are getting more sophisticated in where they are looking. They are going to get more targeted because they can profile people and their trends more easily with social networking sites."

Meanwhile, most new malicious URLs -- 98 percent -- were hosted in the U.S. due, in part, to the location of Web 2.0 services there, according to the report.

Disasters were the No. 1 news event to poison Internet searches in Q1, led by the Haiti and Chile earthquakes. Also abused were the Toyota recall, iPad, and NCAA March Madness searches, according to McAfee. The McAfee Q1 2010 Threats Report is available here.

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