In these days of much email usage hacking of passwords is frequent. So, security of email accounts has become of utmost importance to everybody using them. Gmail has come forward to offer its users a safe and secure process like that used by Internet banking services. It is a two step verification feature that identifies you as the real owner of the account. The first verification is done by using the password that you enter and the second one is done with a code sent by Google to your mobile phone through SMS. To opt for this double security service, enter 'Using 2-Step verification' through your Account settings, Personal settings and Security. It takes about only 15 minutes for the enrolling process. After enabling the verification, each time you log in a code will be requested. Then the code sent to the mobile should be entered before being allowed into the account usage.
Read about this security feature here:
Advanced Sign-in Security for Google Accounts