what is user is using a public computer?
is there a way for the users to erase their log?
I take it you mean that one of your operators is using a public computer? All chat transcripts are secure and are stored on Olark servers. Any transcript can be deleted of you wish, but none are public at any time or in any way.
On the user side cookies are set that will expire shortly after the browser window is closed and the chat terminated.
Olark user waveapps says…
What is the time to expire?