"Web ads are becoming a delivery system of choice for hackers seeking to distribute viruses over the Internet.
In a development that could threaten the explosive growth of online
advertising, hackers have started to exploit security holes in the
online-advertising chain to slip viruses into ads. Just going to a site
that shows such an ad can infect a user's computer.
In May, a virus in a banner ad on tomshardware.com
automatically switched visitors to a Web site that downloaded "malware"
— malicious software designed to attack a computer — onto the
visitor's computer. ScanSafe Inc., one of the first security firms to
discover the virus, estimates the banner ad was on the site for at
least 24 hours and infected 50,000 to 100,000 computers before Tom's
Hardware removed it."
Article Link: http://online.wsj.com/public/article/SB1184806085008…
