In response, Google said Wednesday that it is adding technology to Gmail that makes it harder for employees to send business data out the door. Specifically, the tech giant is bundling a service that helps prevent sending sensitive information through Gmail, at least for customers who pay for the Google Apps Unlimited edition.

With this addition, corporate IT staff can set up a scan of outgoing email (both the text itself and attached documents) for credit card numbers, social security numbers, etc. Messages that trip the switch can be quarantined for review, or returned to the sender along with a prompt to remove the information. Administrators can also set up automatic scans that would flag emails that include certain keywords.

Protecting against data leakage is hot now. While many companies fear hackers will break into their computer systems and steal data (like the Sony hack last year) they may be better off focusing on people already on their networks.

It is far more likely that employees will email information to themselves or download it onto a flash drive—for legitimate or not-so-legitimate reasons—than it is that some outsider will break in.

And that’s why more vendors are pushing into what’s known as data loss prevention. Google already lets IT staff keep fellow employees from downloading, printing, and copying documents containing certain types of data from Google Drive. Meanwhile, Microsoft (MSFT) offers data loss prevention in its Exchange Server and Exchange Online email products.

Startup DataGravity sells a storage appliance that gives them more information about the data they have in-house so they can better ensure that it cannot be downloaded or even viewed by unauthorized personnel.

Google (GOOG) decision to add data loss prevention to its email service comes as it tries to sign up businesses to its corporate-focused products (it claims two million paying customers). But it’s still unclear if Google’s leadership has made Google Apps for Work a priority in light of the company reaping the bulk of its billions of dollars in revenue from advertising and search. And critics said Google needs to do a better job selling into big companies where it competes with Microsoft.

Google also said it will add data loss prevention to Google Drive cloud storage next year.

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