DNS pollution and DNS hijacking are two different DNS attacks or problems with different nature and impact:

　　DNS pollution:

　　Definition: DNS pollution refers to interfering with the normal domain name resolution process by adding false or malicious DNS records to the DNS server. This can cause users to be redirected to the wrong website or service.

　　Cause: DNS pollution can be caused by malicious attacks, configuration errors, or insecure settings. Attackers attempt to subvert the correctness of DNS resolution in order to deceive users or redirect them to malicious sites.

　　Impact: DNS pollution can cause users to visit fake websites, which may harm user privacy and security. It is usually an act of conscious malice.

　　DNS hijacking:

　　Definition: DNS hijacking is a DNS attack in which an attacker hijacks or tamperes with a user's DNS request and redirects it to a malicious site. This is usually achieved by modifying the settings of the DNS server.

　　Reason: DNS hijacking is usually caused by a DNS server being compromised or infected by malware. Attackers attempt to control the DNS resolution process so that users can access malicious sites they control.

　　Impact: DNS hijacking will cause users to be redirected to malicious sites, which may involve malicious advertising, fraud, attacks, etc. It is often a covert form of attack that may not be easily detectable by the user.

　　To prevent DNS pollution and DNS hijacking, similar defensive measures can be taken, including using a trustworthy DNS server, enabling DNSSEC, regularly reviewing DNS configuration, using network security policies, etc. In addition, network users and administrators should remain vigilant and promptly detect and respond to DNS issues to ensure network security and availability.