If you're not sure, verify the URL. Microsoft and Google have large payrolls, but the search giants don't employ literal armies to review ad submissions. If you're at all suspicious of an ad's legitimacy, check the URL via a service such as hpHosts, which tracks domain names that researchers have reported as malicious.

Help vendors by reporting malicious advertisers. To report bogus ads on Google, e-mail security at google.com. This is likely to be more effective than reporting the site via the search giant's online form. If you discover malware purveyors advertising in Bing's results, e-mail secure at microsoft.com. Yahoo, however, offers only a Security Phishing Report Form.