My usb mouse has been working for years without a hiccup, but since about a week or so, I've been experiencing what I would call a second phantom or ghost click, for no apparent. Let me illustrate what's happening:

I clicked each number button in the calculator just once, not too quickly. When I clicked 5 and 8 there was an immediate second click coming from nowhere as you can hopefully tell by the screenshot. This is essentially what's happening. There's no fixed pattern, it just happens every few clicks.
I realize this question might be a bit wide, but I have not been able to find the root cause nor any hint that leads me there. It doesn't look like this is a hardware issue though. What should I be looking into?
I make heavy use of hibernation by the way; not sure if this might be relevant at all, but I have had my share of issues hibernating for weeks in a row with windows 7.
2 Answers
Try plugging in a different mouse (borrow a friend's if you only have one) and see if this (temporarily) fixes the issue. If it does, and I suspect it will, you need a new mouse.
1This is almost certainly a hardware issue. Junk gets inside your mouse and clogs things up, and can cause erratic operation of the tiny switches that make a mouse click. Open it up and clean out all the accumulated lint, hair, crumbs, etc. If you haven't done that in a few years, you will probably be amazed at the amount.