If you jailbreak your iPhone then you must change root's and user moblie's passwords.
I'm posting this story because I did not see this warning when I jailbroke ;-)
Having said that, I didn't and ended up with the ikee worm.
What was happening is that I could not ssh into my iPhone. whenever I tried I got the error:
ssh_exchange_identification: Connection closed by remote host
So I Googled it and found this link:
http://forums.macrumors.com/showthread.php?t=831009
At the end of the day what had happened is that because I had not changed the passwords, the ikee worm was, amongst other things, removing my /usr/sbin/sshd daemon
So be warned, change the passwords!
These procedures worked for me: (I didn't use mobile terminal, I used ssh on the iMac)
http://cydia.saurik.com/password.html
I removed the worm using ideas from these procedures:
http://forums.justcommodores.com.au/lan-lounge/118975-iphone-ikee-worm-fix.html
You may also want to disable ssh (using SBSettings) when you don't need sshd.