This is the result of an online advertising approach known as site retargeting which tracks your online behavior to offer you targeted advertising. At first glance, this may seem like it is posing a security threat, but there are assurances that tracking is done anonymously.
Site retargeting is based on a pretty simple concept. Whenever you visit a website that may want to show you an advertisement, it puts a digital tag called a cookie on your browser. Then, when you visit another site with an area to display paid advertising, the information on that particular and other tags is used to choose an advertisement you would likely be amenable to click or watch. The hope is that, while you may have missed an opportunity to purchase an item once, you may be more inclined to complete a purchase at a later date.
If you don’t appreciate being such a target for advertisers, there are ways to block and delete cookies and to stop ads from reappearing. To delete existing cookies on your browser, choose the option to delete cookies under the settings. Also, if you see an icon that says AdChoices next to recurring advertisement, you can click that icon to stop the reappearance of that particular ad. Most browsers also have a Do Not Track option in their settings, which prevents your browser from being tagged in the first place, but that also means you can’t save passwords or use other tools that are also dependent on cookies. You could also surf the web in private browsing mode (accessible through your browser’s settings) or use an ad-blocking service like Ghostery or AdBlock Plus.