The current version of CamStudio apparently is packaged with some nasty advertisement software.
So to get around this, instead of downloading at: http://camstudio.org/
Download direct from source forge at: http://sourceforge.net/projects/camstudio/
If you get this error: “This application has failed to start beccause of MSVCR100.dll was not found. Re-installing the application may fix this problem.”
Then install this: https://www.microsoft.com/en-us/download/details.aspx?id=5555
Finally I always suggest getting Cam Studio’s lossless codec from the camstudio site (which links to sourceforge) http://a.fsdn.com/con/app/accelerator/button?button_size=small