Each day, over 3.5 billion queries are entered into Google’s search engine. Add billions of posts on social media per day, and it becomes clear that the most dominant way we access online content is through search engines and shared links. The 'surface web' that we use every day, however, is estimated to be less than a thousandth of the entire web! The rest is in the 'deep web': invisible content not indexed by search engines. It contains databases, password-protected websites, intranets, academic journals, and archives, some of it being accessible through specific applications or with credentials.