If your identity has not yet been stolen, the NYTimes has an article titled "Equifax's Instructions Are Confusing. Here's What to Do Now." [0]
tl;dr: Freeze requests for your credit data at the big 3: Equifax [1], Experian [2], and Transunion [3].
(Note: these services may require multiple attempts, some persistence, a service fee, or a phone call to an automated system. YMMV.)
[0] https://www.nytimes.com/2017/09/08/your-money/identity-theft/equifaxs-instructions-are-confusing-heres-what-to-do-now.html
[1] https://www.freeze.equifax.com/Freeze/jsp/SFF_PersonalIDInfo.jsp
[2] https://www.experian.com/freeze/center.html
[3] https://www.transunion.com/credit-freeze/place-credit-freeze
EDIT: missing word