Trojan:Win32/Vundo.gen!H is a component of Win32/Vundo - a multiple-component family of programs that deliver 'out of context' pop-up advertisements. They may also download and execute arbitrary files.
Vundo is often distributed as a DLL file and installed on an affected machine as a Browser Helper Object (BHO) without a user's consent. This family uses advanced defensive and stealth techniques to escape detection and to hinder removal.
There are no obvious symptoms that indicate the presence of Trojan:Win32/Vundo.gen!H.