can two people be logged into the same account simultaneously?

[Dividix]

that is, can two guys who both know user name and password ssh into the same account at the same time?

If not, what will happen if the second guy tries to do that, after the first one has logged in?

If yes, how will it work? What will both of them see on their telnet/ssh clients when the other guy does typing and command execution?

[coopstah13]

the same user can have multiple ssh sessions open, I do that all the time at work, I have sometimes as many as 3 open sessions, the output for anything executed over that session is confined to that session, the other sessions will not see what the "other guy" is doing

[slimx3m]

every time you login with the same username through ssh it will be treated as a new user that just logged-in. so', neither will be able to see what they are typing, unless they check for any type of logs on the system.