Apple announced a security update for OS X 10.6.4 which has addressed an issue which could allow a remote attacker to gain access to shared folders without a valid password.
Security Update 2010-006 was issued yesterday afternoon and it applies to OS X 10.6.4 and X Server 10.6.4. The 1.93MB file is available, as always via the software update option within the operating system. If you want to grab it directly from Apple then you can do so over here.
This security update is an important one for users of Snow Leopard as it will stop a remote attack gaining access to shared folders on a system, but only if they knew the account name on that system. This security problem only affects users who have file sharing enabled.
KitGuru says: Users running an OS earlier than Snow Leopard will not be affected.