Many antiviruses are having ad block components built onto them . I personally use kaspersky internet security and it has a module called banner and ad blocker . It blocks all ads except Google ads ( they also can be disabled ). I think Google ads are not disabled(by default) due to correct targeting that help the user to find out suitable products . These antivirus softwares are going to be a real threat to webmasters running advertisements in their sites. What you think?? Have experienced any set back in ads revenue either ??