Alexandra Elbakyan a23-year-old student of Kazakhstan University has created Sci-Hub, a digital repository housing copies of 64.5 million scientific journal articles. In 2016, the website claimed to services over 200,000 requests per day. Elsevier has filed a case against her as 97.3 percent journal articles stored behind all paywalls are present on sci-hub.org.
Sci-Hub is a web scraping program. Users go to the site, enter the URL, DOI, or text search identifying the article they want. The website searches its archives of articles stored on its servers and those stored on LibGen. If it is not available, it goes to its vault of known usernames and passwords acquired from academics with legit access, pulls up the article you requested giving you a copy and storing a copy away on its servers.
Reference link: https://www.thedailybeast.com/is-this-science-hacker-a-heroine-or-a-villain