I've been paid a big bonus in my last pay and I know my company has made mistake - I changed roles, and I don't know what they've done but it's along the lines of them paying me my full years sales commission, despite already being paid it quarterly throughout the year. It's about 2 months salary. I work for a huge company with complex bonus/sales commission rules and I'm pretty confident they would never notice or ask for the money back if I said nothing. The money would be nice, since I've already quit to be a full time carer for my disabled son and going forward things will be very tight (I'm just working out my notice). I had to take 6 months unpaid leave already this year to care for him, another reason why the money would be handy and also why I'm confident I'm not entitled to the bonus!
I'm a good honest person so I've already told HR and they are looking into it. I assume they will rectify their mistake and ask for the money back, although I suppose there's a chance the admin will be more hassle than it's worth and they'll let me keep it! It did make me wonder though, how many people would be this honest/stupid?