Search-engine poisoning has been the bane of many Internet users existence for a long time. One of the main problems these days is the use of legitimate-looking ads that direct users to malicious sites rather than sites to download applications such as Flash or Firefox. In this case, a search on Bing for Adobe Flash turned up an ad pointing users to a site where they can supposedly download Flash 10.0. Of course, what those users get isn t Flash, but a kick in the digital teeth in the form of the ZeroAccess Trojan.
Source: https://threatpost.com/malicious-ads-bing-lead-zeroaccess-trojan-101411/75756/