Oversensitive mouse issue.

I'm using Ubuntu MATE 16.04 on an older desktop.

Some time last week, my mouse started to behave rather oddly. It now frequently double clicks when I single click. It's an issue I've experienced with previous Ubuntu versions.

Anyway, it's not critical, but it is a tad aoying. If somebody could tell me what the issue is and how to fix it, I'd be most grateful.