Page hijack is a technique exploiting the way search engines interpret certain commands that a web server can send to a visitor. In essence, it allows a hijacking website to replace pages belonging to target websites in the Search Engine Results Pages.
If we simply tell page hijacking is a form of search engine index spamming. It is achieved by creating a rogue copy of a popular website which shows contents similar to the original to a web crawler, but redirects web surfers to unrelated or malicious websites. Spammers can use this technique to achieve high rankings in result pages for certain key words. That means Page hijacking is a form of cloaking, made possible because some web crawlers detect duplicates while indexing web pages. If two pages have the same content, only one of the URLs will be kept. A spammer will try to ensure that the rogue website is the one shown on the result pages.
One form of this activity involves 302 server-side redirects on Google. Hundreds of 302 Google Jacking pages were said to have been reported to Google. While Google has not officially acknowledged that page hijacking is a real problem, several people have found to be victims of this phenomenon when checking the search engine rankings for their website.
Once a hijack has taken place, a malicious hijacker can redirect any visitor that clicks on the target page listing to any other page the hijacker chooses to redirect to. If this redirect is hidden from the search engine spiders, this can be sustained for an indefinite period of time.
Possible abuses for Hijacking are Make "adult" pages appear as CNN pages in the search engines, set up false bank front ends, false storefronts, etc.