Definition - What does DNS Hijacking mean?
DNS hijacking is a malicious exploit in which a hacker or other party redirects users through the use of a rogue DNS server or other strategy that changes the IP address to which an Internet user is redirected. DNS hijacking can leave users unaware of where they are going in terms of using specific servers during an Internet session.
Techopedia explains DNS Hijacking
At its worst, this can lead to various fraudulent practices like phishing or data scraping, where data is collected in dishonest ways. A "softer" version of DNS hijacking is where an ISP will redirect a user to another page to generate ad revenue. For example, when typing in a bad URL, instead of getting a DNS error, the user might go to the ISP search page where the ISP is actually getting paid for sending the traffic.