is it permissible to do online chatting with unknown people concealing own identity as it has become common practice nowadays.what are its repurcussions.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

It is permissible for a man to chat with a man whom he does not know, and for a woman to chat with a woman whom she does not know if the discussion meets the Islamic pre-conditions and is free from prohibitions, like lying, backbiting, slandering, obscene words, and so forth.

As regards concealing one’s ID, if you mean that a person informs the one to whom he is speaking that his name is so and so, whereas in reality it is not his real name, then this is a lie and it is forbidden. However, if you mean that one uses a symbol for the speaker –as is the case in e-mail addresses –then this is permissible.

Nonetheless, we warn against what is spread in those chats, whereby a man chats with a non-Mahram woman, and a woman chats with a non-Mahram man, then this matter leads to many prohibitions as we clarified in Fataawa 85359, 84874 and 81671. 

Allaah Knows best.