Hopper virus infects .VBS files and Word documents, as well as HTML files. VBS/Hopper.A infects other .VBS files by prepending it's code to the original file.
Disinfection & Removal
Some variants of this virus family also infect HTA and HTT files. Some of them lower the security settings of IE's zones. To ensure that the virus works on all platforms, when infecting VBS and DOC files, it comments out the HTML-specific part of itself. It infects documents when closes them.
Some variants of VBS/Hopper are able to infect Excel files as well.
Technical Details: Katrin Tocheva, F-Secure