You have Windows Automatic Update to keep windows itself up to date, and if you remembered to opt in to it maybe you've even upgraded it to Microsoft Update to keep your Office programs up to date too. ...and some software like Firefox and Java have their own updaters, if you didn't disable them to keep your performance up...
But what about all the other programs you run? do you know you are upto date?
Secunia will tell you.
You can go to their web portal for a free scan of your system any time you like, and it will check it all for you. If you are using it at home you can download Secunia PSI (Personal Software Inspector) or if it is for business use there is the cooler sounding Secunia CSI (Corporate...) at a cost, but well worth it.