Opachki is one of many tools developed by criminals to hijack and exploit Windows users search traffic using affilate-based search engines. Instead of only hijacking search result links, it hijacks as many links as it can on any page, using the text enclosed by the HTML HREF tag as a faux search phrase when redirecting the user to an affiliate search engine. The tool is often used by well-known and respected search engines that are ultimately sponsored by advertisers.
Source: https://threatpost.com/inside-opachki-link-hijacker-trojan-103009/72931/