When consumers purchase new devices such as tablets, computers, and laptops, there is pre-installed software and apps ready to go and be used. Vendors get paid to add this stuff to the device, but many people refer to it as crapware they don't need.
Also, think about free software programs you installed. Some may come with toolbars and browsers or related programs they install at the same time. These can have spy programs that collect information about how you use your computer.
Prevention is key to avoiding software you don't want. When you install something while online, pay attention to what files are actually being downloaded. Select programs carefully and try to avoid the quick install option so you can really see what is being downloaded. You may answer 'Yes' easily to something when prompted, but pay attention as it could actually be you giving the software permission to download crapware you don't need.