"New identity" button in Vidalia is misleading and should be renamed.
Vidalia's "new identity" button creates a new circuit by issuing a NEWNYM request to Tor.
This is confusing for users because in Torbutton in the Tor Browser there is a "new identity" option which does something different (it also clears session data which could be used to link two identities).
Vidalia's "new identity" should be renamed to reflect the fact that merely issuing a NEWNYM isn't enough to prevent two identities/sessions from being linked.
I suggest calling it something like "new circuit" or "change exit IP address" etc.
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