For the protection of your account and your client information, we encourage you to sign-up for two-step verification of your Google Account.
You will associate one or more phone numbers, typically your cell phone, which Google servers will call with a verification code if you try to sign-in from a new computer or device. Each device is authorized for sign-in by that account for a period of 30 days, after which another server phone call (or text message) will be made for re-verification. This process ensures that in addition to your password, one more step is used for verification, thereby protecting your account against unauthorized access.
To set it up, go to https://www.google.com/settings and click on Security in the left panel and then select 2-step verification.
We also recommend registration of your phone for lost or reset password help.