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.
WebNexus is an adware program that shows popup and popunder ads. WebNexus is normally installed through trojan downloaders or bundled with other software. WebNexus creates a registry value "winsync" in your registry, the file along with the program is very difficult to remove since its not removable through Add/Remove programs.
Technical details (How to remove WebNexus(pop up))