On June 16, the United Kingdom's incident response team, the National Infrastructure Security Co-ordination Centre, warned that stealthy Trojan-horse attacks were targeting specific U.K. companies and government agencies. However, similar attacks aimed at other countries, including the United States, have been detected over the past year, according to security firms.

This week, security company Symantec sorted through low-volume e-mail threats submitted to its response team for analysis and found several that had targeted U.S. government agencies or had been submitted to Symantec from government sources in the United States. (Symantec is the parent company of SecurityFocus.)

"This appears to be a very specific virus writer targeting government agencies and, not as (other articles) suggested, targeting only U.K. government agencies," said Dave Cowling, senior business intelligence manager for Symantec.

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