Go to the security settings of your mailbox (if you still have access to it). For example, if you use email www.mail.ruthe address of the tab's security will be as follows: http://win.mail.ru/cgi-bin/security?1977996848. View, c IP addresses have been made the last entry in the mailbox. Then go to one of the WHOIS services (e.g., www.ruszone.com/whois/ip.php). Find out who pinned this IP address. It is likely that in this case you will not receive comprehensive information about the end user, but still significantly narrows the circle of suspects.
When registering a mailbox, send an email to the administration email with a request to follow your account. The administrators in this case will put on your account program, prohibiting entry from other IP addresses. Depending on the mail service, this service may be chargeable. In some email services the settings can use and the user in the tab "Security" (e.g., placing or removing the check box for the option "Session only with a single IP address on www.mail.ru).
Go to the website http://lantricks.ru and use one of the programs posted on this page to gather more information about the IP address or the site from which there was a break. After that, contact your Internet service provider serving the IP address and the website with a request to take appropriate measures to prevent further unauthorized access to information. It may happen that you will be denied, but you can negotiate and informally.
Find out the computer name on the network and using more simple method. Press Win +R. In the search line window that appears type "cmd", click "OK". At the command prompt type "nslookup" the IP address of the computer whose name you want to learn, press enter.
Refer to methods of protection against fraudsters and hackers on the websites of well-known bloggers, for example, www.igor-belkin.ru.