ICQ was as unsecure as any chat protocol can ever be. No encryption, plaintext, lots of bugs, HTML and XSS injection and other things, let alone RCEs that directly execute .exe files and were able to steal Browser/Trident engine cookies and active sessions on websites you visited.
Please, just get over it and use jabber/pidgin and OTR encryption if you want oldskool chats.
I don't, and have a question:
If it's reimplementing the protocol, how are old accounts verified? Is there a repository of password hashes that's been shared?