This happens often, whether I'm on the web or in Excel or Word. What is causing this automatic typing?

Thanks

Typing words or a string of letters? Could be a stuck keyboard.

Otherwise - what is being typed? Words? Sentences?

It could be a fault in the motherboard or the software if you bought it legitimatly contact Microsoft it could be someone playing a joke if your connected to the web there is software that allows you to be on someone else's p.c it could also be spyware or adware so run a virus scan and get an incription on your login details I would recommend a 128 bit encription as it would take a super hacked about 5 years to get in and that should solve your problem

Someone mite put a program in your computer
Witch controls your computer and is getting free internet