Our website, our mobile application, and the emails that you receive from Vanguard may use an application known as a web beacon (also known as a pixel tag or clear gif). A web beacon is a tiny transparent image embedded in a web or mobile application page or an email to measure usage and activity. In some cases, a web beacon triggers the placement of a persistent cookie on your device.
We and our service providers may use web beacons and cookies to determine whether and when you receive and open our emails; these beacons and cookies may also capture information about the type of device, operating system, email program, and web browser used to view the email, the IP address from which you opened the email, and whether you click any links in the email. These technologies enable us to gauge the effectiveness, relevance, and value of our email communications, as well as to target relevant advertising to you and to measure the impact of that advertising on your Vanguard relationships.
If you are a Vanguard investor who has registered for secure online access to your Vanguard accounts, we are able to combine the information we collect about your usage of our website or mobile application during a secure (logged-on) session with other information we know about you, such as any account transactions you conduct during your session. We can also identify your computer or device on each online visit to Vanguard, even if you do not log on, and link information about that visit, as well as Vanguard ads that you may have viewed on other websites, to you. We may use this combined information to assess the appeal and usefulness of the information and tools offered on our website and in our mobile application and the effectiveness of our online advertising, as well as to identify Vanguard products and services that may be of interest to you.
Source : https://investor.vanguard.com/investing/privacy-policy