login_screen.tcl in aMSN (aka Alvaro's Messenger) before 0.97.1 saves a password after logout, which allows physically proximate attackers to hijack a session by visiting an unattended workstation.
aMSN (aka Alvaro's Messenger) allows remote attackers to cause a denial of service (client hang and termination of client's instant-messaging session) by repeatedly sending crafted data to the default file-transfer port (TCP 6891).