Often times, people notice a new toolbar has been added to their web browsers with no clue as to how they got there. You may or may not have noticed the trend of app installations including additional software. They are sometimes a little sneaky in hopes that you will quickly click through the Yes/Next/OK buttons without reading.
As you can see in this Java update, there's a pre-checked box for installing the Ask Toolbar.
Another common one is Adobe trying to slyly add Chrome to your Reader or Flash installation. I'm a little more biased on that one as I actually recommend giving Chrome a try. Ask Toolbar? No thanks! Keep your eyes peeled before flying through those installation steps!