Another problem with online ads is malicious ads. Sunday the New York Times placed the following warning on its website:
Some NYTimes.com readers have seen a pop-up box warning them about a virus and directing them to a site that claims to offer antivirus software. We believe this was generated by an unauthorized advertisement and are working to prevent the problem from recurring. If you see such a warning, we suggest that you not click on it. Instead, quit and restart your Web browser. Questions and comments can be sent to firstname.lastname@example.org.
Some additional information can be found here .
According to the second link the New York Times believes it has eliminated the problem (although I encountered one of the malicious ads after reading the first warning). Even so this sort of thing hardly encourages readers to trust online ads. If the New York Times can't manage to keep malicious ads out of their online newspaper why should anybody trust any online ad. A TV commercial may be annoying but it is not likely to hijack your TV.