I don't know exactly the cause of this problem (I'm pretty sure it's a malware) but I found a very succesfull solution.
There are two ways:
The first way is to remove totally
firefox, including all the personal configuration files. You have to go to the control panel-> applications and unistall firefox from here. Then you have to delete the other 3 directories that contain the configuration file and (i think) the real problem.
These directories are (on vista) on C:\users\XXX\appdata\roaming\mozilla
and on XP (if I remember well) C:\documents and settings\XXX\appdata\roaming\mozilla
and C:\documents and settings\XXX\appdata\local\mozilla
and the mozilla directory C:\program files\Mozilla Firefox
Note that XXX is your username that you use to logon. If you cannot find the directory appdata, maybe you have the "show hiddens files and directories" unchecked. To check it you have to go on file explorer on Tools->Options then you have to click on view and check "show hiddens files and directories".
Then you have to Install again firefox and to go (when firefox is totally started) to Tools->Options->Privacy and uncheck "Accept cookies from third part" (i'm not sure it is writtens as i wrote because i've the italian version of firefox). I'm not sure this will avoid Yoog's back, but I red it on a blog somewhere over the internet.
The second way is to delete theese files that remained me after the uninstallation. Theses files are (in the firefox directory):
Directory -> Components
Directory -> defaults/pref
Directory -> extensions
Directory -> plugins
All files except npnul32.dll
This second way may damage some plugins and the correct working of firefox, so i suggest the first that i tested and works. Good luck. I'm not responsible for any damage to your computer.
Windows Defender recognize nsdcads.dll as a virus. Maybe only this file need to deleted to resolve the problem.
I also discovered that yoog create a registry key. To eliminate it open the command prompt and edit regedit
. Then click on Edit->Find and type Yoog. If yoog registered into your registry regedit (this program) should have found 3 key on the left. Right click on each of them and click Delete. This will delete the registry codes.