Funny old world!
Yesterday I swapped out the cordless mouse for a wired one and the problem went away.
This morning, I thought, I better get the wireless mouse and remove the battery before we find it corroded away in 3 months time. So I fetched the mouse and its receiver and I noticed that it moved the pointer on MY computer when I put it down on my desk. So, I had a mouse in each hand and both were driving my pointer.
This is the first time there has been a conflict in a few years. So, I re-matched one mouse to my receiver and now only one mouse works my pointer. For reasons which are now clear, the matching process changes the channel everytime you re-match the mouse and receiver to each other. Neat but confusing when it gets it wrong.
Rans6.......