I recently obtained another computer at work after my hard drive crashed. It was used by a former co-worker, but it never had Microsoft Office installed. Since I needed Excel for several programs I use, I installed Office 2003. This morning I noticed an Office update, but didn't read what it was. I downloaded and installed it, then restarted my computer. When I opened Excel, it opened in Office 2007. I checked what the update was, and it was a service pack for Office 2007. I now have Office 2003 and 2007 on my computer.

How can it update a program I never had? As far as I know, there was never even an evaluation version of 2007 on this computer. The former co-worker used OpenOffice.

Any ideas how this happened?