and i can't understand why network shield scans jpg files!
6. Can JPEG, GIF, and other image files be infected? Yes. Some software programs have vulnerabilities that contaminate JPEG files with malicious code. Contaminated JPEG files can carry or launch a virus, worm, or Trojan on unpatched systems.
http://www.mcafee.com/us/mcafee-labs/resources/threats-faq.aspx#6

http://antivirus.about.com/od/virusdescriptions/a/perrun.htm