Eye-tracking studies have shown that Internet users often ignore web page zones likely to contain display ads (sometimes called "banner blindness"), and this problem is worse online than in offline media. On the other hand, studies suggest that even those ads "ignored" by the users may influence the user subconsciously.
Fraud on the Advertiser
There are numerous ways that advertisers can be overcharged for their advertising. For example, click fraud occurs when a publisher or third parties click (manually or through automated means) on a CPC ad with no legitimate buying intent. For example, click fraud can occur when a competitor clicks on ads to deplete its rival's advertising budget, or when publishers attempt to manufacture revenue.
Click fraud is especially associated with pornography sites. In 2011, certain scamming porn websites launched dozens of hidden pages on each visitor's computer, forcing the visitor's computer to click on hundreds of paid links without the visitor's knowledge.
As with offline publications, online impression fraud can occur when publishers overstate the number of ad impressions they have delivered to their advertisers. To combat impression fraud, several publishing and advertising industry associations are developing ways to count online impressions credibly.
Because users have different operating systems, web browsers and computer hardware (including mobile devices and different screen sizes), online ads may appear to users differently from how the advertiser intended, or the ads may not display properly at all. A 2012 comScore study revealed that, on average, 31% of ads were not "in-view" when rendered, meaning they never had an opportunity to be seen. Rich media ads create even greater compatibility problems, as some developers may use competing (and exclusive) software to render the ads (see e.g. Comparison of HTML 5 and Flash).
Furthermore, advertisers may encounter legal problems if legally required information doesn't actually display to users, even if that failure is due to technological heterogeneity.:i In the United States, the FTC has released a set of guidelines indicating that it's the advertisers' responsibility to ensure the ads display any required disclosures or disclaimers, irrespective of the users' technology.:4–8
Ad-blocking, or ad filtering, means the ads do not appear to the user because the user uses technology to screen out ads. Many browsers block unsolicited pop-up ads by default. Other software programs or browser add-ons may also block the loading of ads, or block elements on a page with behaviors characteristic of ads (e.g. HTML autoplay of both audio and video). Approximately 9% of all online page views come from browsers with ad-blocking software installed, and some publishers have 40%+ of their visitors using ad-blockers.
The collection of user information by publishers and advertisers has raised consumer concerns about their privacy. Sixty percent of Internet users would use Do Not Track technology to block all collection of information if given an opportunity. Over half of all Google and Facebook users are concerned about their privacy when using Google and Facebook, according toGallup.
Many consumers have reservations about by online behavioral targeting. By tracking users' online activities, advertisers are able to understand consumers quite well. Advertisers often use technology, such as web bugs and respawning cookies, to maximizing their abilities to track consumers.:60 According to a 2011 survey conducted by Harris Interactive, over half of Internet users had a negative impression of online behavioral advertising, and forty percent feared that their personally-identifiable information had been shared with advertisers without their consent. Consumers can be especially troubled by advertisers targeting them based on sensitive information, such as financial or health status.
Trustworthiness of advertisers
Scammers can take advantage of consumers' difficulties verifying an online persona's identity,:1 leading to artifices like phishing (where scam emails look identical to those from a well-known brand owner) and confidence schemes like the Nigerian "419" scam. The Internet Crime Complaint Center received 289,874 complaints in 2012, totaling over half a billion dollars in losses, most of which originated with scam ads.
Consumers also face malware risks when interacting with online advertising. Cisco's 2013 Annual Security Report revealed that clicking on ads was 182 times more likely to install a virus on a user's computer than surfing the Internet for porn.
The Internet's low cost of disseminating advertising contributes to spam, especially by large-scale spammers. Numerous efforts have been undertaken to combat spam, ranging from blacklists to regulatorily-required labeling to content filters, but most of those efforts have adverse collateral effects, such as mistaken filtering.