There are actually more than 3 providers and you should put a freeze on everything you can. You only need unfrozen credit for applying for new lines of credit (loans, credit cards, etc), and unfreezing is a quick process (15 minutes or so).

Here’s a pretty comprehensive guide for protecting yourself: https://old.reddit.com/r/IdentityTheft/comments/uvv3ij/psa_freezing_your_three_main_credit_reports_is/

It’s better to take these steps before you get your identity stolen rather than after. These steps can prevent your leaked information from being used against you.