If you opened 3389 port outside by mistake, you might be get log message like ’ +&Cookie:mstshash=hello ', ’ Cookie: *mstshash=A’, '/Cookie:mstshash=Administr’ .
This message means attempting to connect to your computer or server. It is trace of scanning attack
When you search this log on google, you can get result of most attack attempted from Russia IP.
There are 517 scanner attack to 3389 port. Of the 517 attacks, it can be confirmed that there are 392 attacks on the Chinese IP and 26 attacks on the Russian IP.
Port 3389 is for Windows Remote Desktop Protocol (RDP). Bots scan the internet constantly for common service ports like that. Best practice is to never allow access to those services directly from the internet, and to access via a secure VPN connection instead.
Windows remote desktop is by default port 3389 but you can configure it to basically any port not in use, a vpn is indeed the more secure but isn’t available to all users (vpn comes usually with a cost whether you set up one yourself or you pay for a service → I don’t trust free vpns)