Google introduced a suspicious account activity warning system in Gmail back in march 2010. Google just compares gmail login system IP addresses of computers. Gmail logins from different regions in the world, for example the U.K and India in short time would trigger the warning notification, giving Gmail users the chance to react promptly by changing the account password to protect further abuse.
I recommend you to read these 2 articles,
How To Check Whether My Orkut/Gmail Account Hacked or Not ?
How To Get Back Your Hacked Gmail/Orkut/Google Account ?
The above two articles must me know to every Gmail users.
How does this work?
Using the IP address you provide to us, our automated system can determine your broad geographic location. If you log in using a remote IP address, our system will flag it for you. So if you normally log into your account from your home in India and then a few hours later your account is logged in from U.K, you’ll get a notice like the one above at the top of your Dashboard page – alerting you to the change and providing links for more details.
Recently Google rolled out this Security feature to all Google services, and will display suspicious account activity in the Google Dashboard.
Two links are provided in the Dashboard notification message,
1. Details &
2. Change Password.
Check the below screenshot which clearly reveals Gmail login details from different IP address within minutes,
Details opens a small popup with additional information about the account activity listing the location, IP address and date and time. The alert can be ignored or closed in this popup.
The other option is to change the Google Account password, an option that is also provided directly in the initial notification message.
I recommand you to read this article which will guide you to create a strong password for your email accounts.
Stay protected with your Google accounts…