Internet technologies make it very easy to collect all kinds of information about us, from sources like:
Source: Information privacy, Wikipedia
Big Data projects - large collections of data elements from many different sources - make it easy for government agencies, advertisers, corporations, private investigators and individual to put together a lot of personal information about us, to target us and to track our actions.
Data mining and data analytics are big businesses today.
TechTerms explains that the term digital footprint refers to:
"A digital footprint is a trail of data you create while using the Internet. It includes the websites you visit, emails you send, and information you submit to online services."
"An active digital footprint includes data that you intentionally submit online. Sending an email contributes to your active digital footprint, since you expect the data be seen and/or saved by another person. The more email you send, the more your digital footprint grows. Since most people save their email online, the messages you send can easily remain online for several years or more.
Publishing a blog and posting social media updates are another popular ways to expand your digital footprint. Every tweet you post on Twitter, every status update you publish on Facebook, and every photo you share on Instagram contributes to your digital footprint. The more you spend time on social networking websites, the larger your digital footprint will be. Even "liking" a page or a Facebook post adds to your digital footprint, since the data is saved on Facebook's servers.
Everyone who uses the Internet has a digital footprint, so it is not something to be worried about. However, it is wise to consider what trail of data you are leaving behind. For example, remembering your digital footprint may prevent you from sending a scathing email, since the message might remain online forever. It may also lead you to be more discerning in what you publish on social media websites. While you can often delete content from social media sites, once digital data has been shared online, there is no guarantee you will ever be able to remove it from the Internet."
The San Jose Public Library's Virtual Privacy Lab points out that:
"People are comfortable with different levels of privacy in different aspects of their lives. Some want to keep their work and personal lives separate, while others want to avoid government monitoring or prevent corporations from using their data for profit. Some people want to restrict who sees their personal information as much as possible while on the other hand, some are not at all concerned about privacy and freely volunteer their information if it’s convenient or beneficial to them.
To maintain your own privacy and to respect the wishes of others, it’s important to think and talk about privacy preferences and to apply that thinking proactively when you use technology, for example by reviewing privacy settings. Knowing about how online information sharing works, and what the potential consequences can be, will help you make informed choices about privacy."