SEO poisoning, also known as search poisoning, is an attack method in which cybercriminals create malicious websites and use search engine optimization tactics to make them show up prominently in search results. 
The sites are associated with terms that large numbers of people are likely to be using in searches at any given time, such as phrases related to holidays, news items and viral videos. 
According to Websense Security Labs, up to a quarter of the first page of search results for trending topics are linked to malicious websites.