There's a lot of excellent free software out these days. However, a great deal of it is "bundled" with undesirable additional applications that also attempt to install on your system. Once they get on, they can cause all sorts of issues and they can be difficult to remove. So, to avoid these pitfalls you must read the installation dialog boxes carefully, and UNCHECK anything not associated with the target program. Always choose CUSTOM INSTALL, so that you will have the option to pick your components.
Here's an excellent video regarding this subject. Please have a look, as well as making note of the excellent crapware removal programs mentioned such as ADWCleaner and JRT.