Invalid user activity is when a real person interacts with an ad, but not out of actual interest.

Some actions are accidental, like when a mobile user reaches for a link and taps an ad instead. Others are intentional and sometimes downright fraudulent. For example, publishers might ask (or even pay) users to click on ads, watch videos, or view content they wouldn't normally engage with to increase their impression counts.

Traffic caused by deceptive tactics like these creates bad user experiences and provides little or no value to advertisers, which is why we are committed to stamping it out.

Accidental clicks happen, as the name implies, when users didn't intend to click on an ad. They often occur as a result of poor ad placement. For example, ads should be clearly distinguished from other website content, such as menu, navigation, and download links. Please review our Ad placement policies to learn more.

Ad hiding is when ads are placed in ways that make them impossible to see under any normal circumstances. Some examples are ads tucked under iframes, hidden behind content, hidden behind other ads, inside invisible HTML containers, or ads that are displayed but too small to be seen (aka "pixel stuffing").

Ad injections happen when ads are inserted into pages without the publisher’s knowledge and are often created by free wifi applications, browser plugins, and 'software bundles.' Ad injectors provide a poor user experience and potentially cause privacy leaks. This type of attack also steals revenue from publishers.

Ad stacking is when multiple ads are stacked in layers in a single ad space, and only the top ad shows. An advertiser is led to believe that their ad was shown on a web page (or inside an app), when in fact it was rendered but not actually seen (because it's hidden by the top ad).

Botnets are automated software programs that run on Internet servers or hijacked computers. When used for ad fraud, botnets can be programmed to create a large volume of invalid impressions, clicks, and traffic. Unfortunately, they can also be programed to act like real users, which makes their traffic difficult to spot. So in addition to our automated filters and manual reviews, we also deploy specialized research teams to hunt out and stop botnets harming advertisers, publishers and users.

Clickjacking is the use of deceptive elements (e.g., buttons) or interfaces on a web page in a way that a user is tricked into clicking on an ad that they didn't expect to click on. These types of attacks are usually implemented by overlaying an invisible ad unit over a web page element or using code that allows an invisible ad unit to follow the user's cursor.

Falsely represented inventory is based on ad traffic falsely portrayed as coming from high-value users or a site claiming it is a different site.

In-stream video typically represents pre-, mid-, or post-roll ads shown within other video content (essentially these ads are blended into the primary video content). In-stream video can generate invalid traffic when it is primarily based on non-human traffic to videos, in which an in-stream video ad is marked or measured incorrectly as having been viewed by a real user.

Out-stream video is what is typically shown in "display" ads such as banners, interstitials, native (inline) ads, etc (in contrast to in-stream video, which is blended with other video streams). Out-stream video invalid traffic is the misrepresentation and display of in-stream video in an out-stream format. For example, this happens when in-stream video ads are shown in a banner ad -- an advertiser is led to believe that their ad was displayed in-stream with other video content, when in fact it was displayed in a different format.

Malware is any kind of software that's designed to harm a computer. Malware can infect mobile devices to generate various types of fraudulent traffic. This traffic can include hidden ads served in the background (without the user's knowledge) and interstitial ads injected and displayed over a user interface.

Pop-under ads are ads that are displayed in a new browser window that are typically opened under (behind) the active browser window. As a result, the user is unaware that the pop-under ad has been displayed until the active window, or windows are closed. Often this leads to a bad user experience, especially so because it's difficult to determine which web site led to a pop-under ad.

We work hard to keep our own networks free from invalid traffic, but to prevent invalid activity across the web we all need to work together. We believe that industry collaboration is an essential element of the fight against invalid traffic, which is why we collaborate both formally and informally on relevant efforts across the industry. We engage in and participate in key working groups in the IAB Tech Lab and the Trustworthy Accountability Group (TAG), and we also participate in accreditation of our invalid traffic defenses by the Media Rating Council (MRC). In addition to working with these industry bodies, we also collaborate with other organizations through more informal efforts that are mutually beneficial. One example of this more informal collaboration is the takedown of the 3ve ad fraud operation, which entailed collaboration between Google and various other players in the digital advertising ecosystem.