Why do I always See the Same Ads When Visiting Different Websites？
If you like to view online, you might realize you always see the same or similar ads on different webpages from different websites. Is it because your computer affected by virus or does your computer get attacked ?
Let's answer the question directly first since you are wondering: If you are seeing the ads are Google ads which are put by the website owners, you should not be worried about them, those ads are normal. Because those ads content are generated by Google, not by websites and their owners. The ads content are un-harmful.
Why lots of websites display Google's Ads ?
Because of monetization. Google provides a great mechanism and technology to all websites: Just add small piece of code on a webpage, Google can send ad content to that web page and display ad at the specified position in real-time. If any website visitor clicks that ad, a small money will be generated, Google will share the money with website owner, so that the website owner have chances to earn small money to do something, for example, using the money to pay the hosting and domain annual fee, or buy other stuff. If the website is very popular with huge visiting traffic, the Google ad money could be outstanding. This Google ads system called Google AdSense.
How does Google AdSense Generate Ads Content ?
Google generates and sends ads content based on your web page content and your website's audience. When you put AdSense piece code on the webpages. Google's technologies know the content on the webpage; Google also retrieving current website visitor (the audience) 's visiting history data and guess the visitor's recent interests. Actually, Google publishes that they use several ways to automatically deliver ads to target websites which includes Contextual targeting, Placement targeting, Interest-based and language targeting. Please read more details from AdSense official website.
Why Do I See the Same or Similar Ads when Visiting different Websites ?
We mentioned above, the one rule of Google Ad content generating is website's audience and interests based.
Interest-based advertising enables advertisers to reach users based on their interests and demographics (e.g. 'sports enthusiasts'), and allows them to show ads based on a user's previous interactions with them, such as visits to advertiser websites. To complement interest-based advertising, Ads Settings lets users view and edit their interest categories.Google's web browser Chrome (similar on other web browsers) has the way to track visitor's visiting history and interests (visitor can adjust your interests settings.), The visitor's previous visiting data is saved to local cookie, which can be retrieved by Google AdSense technology easily. For example, if you searched airplane fares previously. then you will see more related airplane fares ads displayed in the next time; But due to the ads display polices, the generated ads is limited range for the target website and content, and audience's interests. mostly the visitor will see the same or similar ads even he/she visits other websites since the ads content are controlled by Google AdSense program, not by websites.