Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Network Vulnerability found in OSX Lion –
Some reports from Errata Security have pointed out a new security vulnerability in the latest version of Mac ,OS X Lion. The latest security problem could allow certain users to access restricted network resources without requiring a password.
The vulnerability has got something to do with the LDAP, which is a protocol that email and other applications use to gather information from a server. The problem is most worrying for enterprise environments, as this problem means it is extremely simple for a user to access potentially sensitive files that they other wise would not have access to.
Apple are expected to patch this security hole in OS X Lion 10.7.2. as they missed it in there most recent patch 10.7.1