When you download a free software you must pay attention to “fake” download buttons that often are in free software sites (but not only) like Download.com, Tucows, FileHippo, Softonic, Softpedia, SnapFiles etc…
Just go over with mouse and you can see that the link is not the real for download.
If you click you could be redirected to ads pages or even download software that contains adware/malware.
You must also pay attention to the installation procedure of downloaded software as they can include PUPs (Potentially unwanted programs), like toolbars, background applications that can monitor/trace user activities, etc…
The main raccomandation is to download the software only from official sites of developers.
During installation process can be show various offers of these unwanted software, just uncheck all the checkboxes or click Decline.
To avoid the installation of that junkware you can use the free software Unchecky, it automatically uncheck the checkboxes.
If you had installed that unwanted software accidentally you can use free programs to remove them, there are various one very popular and working good like Malwarebytes, Spybot Search & Destroy, AdwCleaner; they allows you to perform a system scan and the remove the related files and registry entries found.