Adware:Adware (or spyware) is a small program that is designed to show advertisements (in various form and degrees of intrusiveness) on your computer. It often reports personal information back to its owners. As a result your sense of privacy can be violated.
Horst is a Trojan downloader and homepage hijacker believed to originate from the Ukraine. This Trojan secretly installs on your computer. After installation, it will download and install other malicious adware, Trojans, and viruses onto your computer without your knowledge or consent. It may also hijack and inject itself into system processes, using rootkit techniques. This Trojan will log your keystrokes and transmit this information from your computer to its creator. It is highly dangerous and should be removed immediately to protect your personal and financial information!
Technical details (How to remove Trojan.Horst(pop up))