The creator of the malicious ads posed as Vonage, the Internet telephone company, and persuaded NYTimes.com to run ads that initially appeared as real ads for Vonage. At some point, possibly late Friday, the campaign switched to displaying the virus warnings.
Because The Times thought the campaign came straight from Vonage, which has advertised on the site before, it allowed the advertiser to use an outside vendor that it had not vetted to actually deliver the ads, Ms. McNulty said. That allowed the switch to take place. “In the future, we will not allow any advertiser to use unfamiliar third-party vendors,” she said.