I again found on my sister's Windows PC the infamous Ask toolbar, probably installed along with some software. It is easy for bloatware to slip through.
That is just one example. I'm aware that there are ways to specifically block the Ask toolbar but I'm looking for a more general solution.
So I wonder if there is a way to maintain a blacklist to stop such programs from ever getting on the computer in the first place?
I use Winpatrol for this purpose. It's a great program for preventing any unauthorized changes to your system (there is a free version). It runs in the background and watches for any attempt to change the system (install software or toolbars, change the registry, etc.). It presents a window asking whether you want to allow the change and has the option to permanently either allow or deny a specific program. I forget whether you can blacklist a specific program in advance (haven't been back to Windows for awhile, but I keep it installed).
You can look into a program which my High school actually used to solve this kind of issue.
http://www.faronics.com/en-uk/products/deep-freeze/
Basically this program allows you to put in a "preset" allowing you to decide what you want to have installed on the computer, creating an "image" if you want to call it that. Then basically when you reboot the computer, any changes made will revert back to that image you created based on your settings.
