I've found unusual activity where there is an attempt to authenticate but unsuccesfull due to no entry in database (LDAP) but there is accounting record for it. Below are the log & accounting record.

Fri Oct 21 22:03:08 2005
        Acct-Session-Id = "0026190D"
        Framed-Protocol = PPP
        Framed-IP-Address = 61.6.116.27
        User-Name = "assasaas"
        Acct-Authentic = RADIUS
        Acct-Session-Time = 7
        Acct-Input-Octets = 762
        Acct-Output-Octets = 494
        Acct-Input-Packets = 16
        Acct-Output-Packets = 15
        Acct-Terminate-Cause = User-Error
        Acct-Status-Type = Stop
        Called-Station-Id = "20878830"
        NAS-Port-Type = Async
        NAS-Port = 143
        Connect-Info = "28800 V34/V42bis/LAPM"
        Service-Type = Framed-User
        NAS-IP-Address = 61.6.116.2
        Acct-Delay-Time = 0
        Client-IP-Address = 61.6.116.2
        Acct-Unique-Session-Id = "62a6e1512da039e2"
        Stripped-User-Name = "assasaas"
        Realm = "NULL"
        Timestamp = 1129903388