Twitter also knows which websites users visited before going to its site, whether users clicked on multiple pages within a site, the amount of time spent on each site, and occasionally the search term that people used before visiting a website. And, if you’re logged onto Twitter.com on the mobile web, Twitter can also track your activity on mobile sites that use Twitter’s buttons, Reverte added.
There are about 1.5 million websites that have Twitter’s tweet button on its pages, according to BuiltWith.com, a site that tracks the technology websites use. Interestingly, far fewer websites use Twitter’s follow button, which clocked in at 460,667 sites. Approximately 10.9 million websites use Facebook’s like button, in comparison.
Twitter did not respond to a request for comment about its work with social plugins. Given the increasing pressure on Twitter to boost its ad revenue as it tries to woo investors, it would make sense for the company to mine its usage data. Twitter could, for instance, combine the data from plugins with its recently acquired mobile ad exchange, MoPub, to further enrich its ad targeting abilities.