When you work as a freelancer, employers who are on top of their accounting game will always ask you for a signed W-9 form before they pay you the first time. The W-9 form, AKA “Request for Taxpayer Identification Number and Certification,” provides your employer with the info needed to send you a 1099 form, which is used to report your income to the IRS.

Most freelancers just use their Social Security number as their tax ID number on the W-9. This is a big mistake, unless you really, really trust the company you’re working for. That W-9, after all, contains your legal name, Social Security number, and current address—three of the key pieces of data a thief needs to steal your identity.

Many businesses, both small and large, fail to take reasonable security measures when handling W-9s. Your W-9 might be sent across the Internet via unencrypted email, or stored on insecure computer networks, where unscrupulous employees or hackers could gain access. As we saw with the Sony Pictures hack, even large corporations are not immune. And as you do more freelance gigs (and send more W-9s) the risk multiplies.

Protect yourself right now by requesting an Employer Identification Number from the IRS. You can use this number on a W-9 in place of your Social Security number. To apply, go to this page on the IRS website and click the link at the bottom that says “APPLY ONLINE NOW.” (Bafflingly, the online EIN application form only operates between Monday and Friday, 7 a.m. to 10 p.m. Eastern time.)