This has happened to me 3 times in the past year. It appears to be a Microsoft issue and it just happened again when the last updates installed for Windows.
And yes, next time I am getting a MAC!
It deletes words as I type - and it doesn't matter whether it is in a forum like this, in a text file, Word ... any program that requires writing is vulnerable.
The cursor not only affects writing, it will also shift files in whilst within Windows explorer. It also shifts icons around desktops and deletes files at will.
No anti-virus picks anyhting up. So I have to backup nearly over 500GB of data ... it sucks! It also highlights text and does obscure things like it just did now - and changed the background colour to grey ... can't see how it did it.
It is not the touchpad either - I do not have to even touch it!
Now it is white again ... damn Windows fremlin has got to go ...