The idea behind these types of messages is to try to entice you to sign up to an exchange - why?
Farm your credentials
Try these credentials on other exchanges (real ones)
Steal your crypto
It also allows them to try your email/password combo on other sites such as email, etc. If they have access to your email accounts, they can access almost anything.
Another move they try is to get you to deposit real money/crypto into the account to "verify" yourself and "enable you to claim" - you won't be able to claim the crypto you have won. They WILL keep your deposited crypto/money.
This is a scam.
If you have registered for this scam, these are the following steps you should be taking:
1) If you used the same e-mail as you normally do, but a different password. You are fine.
2) If you used BOTH the same e-mail and password as on other websites. CHANGE YOUR PASSWORDS! Any other service with the same Username/Password is AT RISK
Start with your e-mail account.
Next, Crypto exchanges with the same username/password.
Next, Accounts with the ability to buy things. Amazon/PayPal/Bank, so on.
Next, General Accounts. Social Media etc.
3) If you deposited to try and claim that giveaway, that Crypto is gone. Accept it. Move on. It might be hard but it must be done.
4) If you have submitted any sort of I.D. for verification. Treat it as though your wallet has been stolen. Make a police report so should your identity be stolen and used for something, you have a reference to say its not you. This will resolve any issues that come up!