If a configurable number of failed login events is detected from the same IP address BotFence dynamically lists that IP address im the Windows firewall as blocked.
If your Windows server is reachable from the internet and you want certain services like remote desktop, FTP transfers or SQL-Server to be accessible from outside then hacking attempts on your server will definitely be made.
Numerous automated hacking tools, called 'bots' are active on the internet. They scan IP address ranges for published services and when they find FTP, RDP or SQL-Server services active they will try hundreds or even thousands of frequently-used passwords. 'Administrator' (rdp) and 'sa' (superuser for SQL-Server) are the most targeted accounts.
As long as the bots don't guess your passwords right you'll probably never now about them, apart from the high server load caused by the thousands of login attempts.