Daniel,
It has been 3 days since your post, did you get this fixed?
I just saw your post and I am guessing you have a laptop and the internal mouse you speak of is the touch pad. and as you drag or move the mouse it is highlighting text or data like when you hold down the left button.
you probably have simply double tapped the pad and it is in a highlight style mode.
hit ESC or close the app and reopen, or it you have to reboot.
If by change you left it alone on friday and are comming back to work on monday try this. otherwise you have probably already fixed it.
Don