It probably wasn’t your (direct) fault Termy. What often happens is that you load a piece of software onto your computer – as we all do from time to time.
Sometimes, there are several ‘tick boxes’ which are on pages shown to you during the installation process – “Create a desktop shortcut” is a typical one or “Create quick launch in the systemtray” (or words to that effect) is another.
Most users simply accept the default option – i.e. the green ticked boxes – and click on “Next” to continue the installation process.
What some software suppliers do (PARTICULARLY the Freeware ones) is to have a box called “Instal Google toolbar” (usually out of your sightline or down in a corner where you may not notice it) and there is already a green tick in the box. Unless you spot this and ‘un-tick’ it, you get Google toolbar installed whether you wanted it or not.
As I mentioned earlier, it is far more that JUST a toolbar put there for your convenience – as the name suggests. It invades your entire internet browsing experience and gives you all sorts of unwanted pop ups amongst other things.
This is most likely how you got in on your computer.