Your messages are cleartext, can be forged, and your password can be trivially grabbed across just a few logins.
It's like pre-https internet basically.
This also means winlink shouldn't be used for PII (which is sort of important in an emergency!).
If you can at least key exchange and encrypt between you and the next node, you have some safeguards and your messages aren't in the clear - but that is currently prohibited by the regs.