If you notice a large increase in the traffic to your website and if after you check the visitor statistics it turns out that it comes from countries across the world or from other web servers, your website is most likely being attacked by an automatic bot. Those pieces of software go through random websites attempting to log in to their admin area by using a brute-force attack or to leave spam comments beneath any sort of article where this sort of an option is offered. The fact is that, that's something quite common nowadays, but if you know the IP addresses from which the attacks come, you can block them, so the bots shall not be able to access your website in any way. Naturally, you are able to block IPs even if you allow only people from certain countries to access your website.