First of all, such a situation is to prevent system protection: antivirus and firewall. If you have not installed, you must install and test the system. Moreover, it is desirable to establish an efficient and optimal means of protection (e.g. Kaspersky Internet Security). But if you have not used such software, possibly malicious, open port has been used dangerous applications.
The easiest way to view the presence of such port with a simple text, which can be performed online at the link: http://2ip.ru/port-scaner/. If the analysis of your computer, you'll find the open port (potentially dangerous for system), it will show red color. If a port in the course of the inspection found, make a note of the name separately because it urgently needs to be closed.
To close such port, you can use many programs. But the most simple is Windows Worms Doors Cleaner, with a volume of only 50 KB does not require installation (you can download it at: http://2ip.ru/download/wwdc.exe). After downloading it just run the malware and close the port that issued the computer analysis after the test. Then restart the computer. However, it is rather the action, so to speak, in haste, as the port may again be opened. Therefore, it is advisable to install a firewall (e.g. Outpost Firewall) and to maintain the status quo after the closure threat of the port.
Also does not interfere with the test computer using a free utility AVZ (can be downloaded from the link: http://www.z-oleg.com/secur/avz). During a quick test, it is necessary to detect errors of the system settings, probably shot down using the same port. For example, if you allow "anonymous user" you should disable it and restart the computer.