(FORTUNE Small Business) – This flu season the most dangerous and costly sickness could strike your desktop.

10,000 new computer viruses are projected to attack Internet users in 2004, up almost 400% from 2003.

Small businesses are twice as likely to be infected, despite spending 5 times more on security per employee than big firms. — LINDSEY GERDES

SOURCES: NATIONAL CYBER SECURITY ALLIANCE, FBI; SYMANTEC SECURITY