Windows 8.1 on MacBook Pro - ghost text

I am running Windows 8.1 with Microsoft Office on my new MacBook Pro.

When I create a new Word document an leave it open for a while, all of a sudden new text appears/is entered although I haven't touched the PC. Really weird, looks like a ghost user or remote entry. When I wait an hour more than one page full of text is entered. This also happens on any other entry filed like Internet explorer or Google explorer or when I write an e-mail.