[ubuntu-za] Font installer blocking updates

[Jan Greeff]

After downloading the Installer for Microsoft True Type Fonts, my system 
refuses to install the package, warning that it's from an untrusted source.

Now this installer is blocking all updates and installations from the 
software center. Also, I do not seem to find a way to remove it.

The updates installation manager does not even allow me to uncheck the 
item in order to install other updates.

Seems like anything related to Microsoft works like a virus on Ubuntu. 
How do I get rid of this bug?

I am running on Ubuntu 12.04.

Jan