If these are logon events for type 3 or 10 logon shown in the security log
then someone is connecting to your computer though I have never seen an
email address in the security log for logon events so I am not sure where
you are seeing that. You need to make sure you are using a properly
configured firewall and use strong passwords for any user accounts. If you
are using cable or DSL connection for the internet I consider the use of an
"internet router" or firewall device an absolute must to protect your
computer/network even if you are using a software firewall that can be prone
to becoming disabled or misconfigured by user interaction or even malware.
You should also be sure to scan your computer for malware and spyware using
the latest definitions for whatever you use to try to get your computer as
clean as possible without a reinstall of the operating system. Also an
insecure wireless network will allow other users to access your
computer/network. WEP is considered very insecure for protecting a wireless
network these days for non 802.1X installations.
Steve
http://www.microsoft.com/athome/security/protect/windowsxpsp2/Default.mspx
--- Protect Your PC tips