I can't vouch for any statistical analysis, but when I last looked at my router logs, I'd see an average of 5 probes (A single IP addresses looking for open ports) a day.  About 40% are Chinese, usually attached to a university, followed by probes from Russia, then other European and US addresses in number.   It's a little unnerving when you are aware that random people checking the lock on your door several times a day.