Slashdot | Windows 2003 and XP SP2 Vulnerable To LAND Attack
"Dejan Levaja, a Serbian security engineer has discovered that nearly 8 years after the attack was first made public, WIndows 2003 and Windows XP SP2 are in fact vulnerable to the historic LAND attack." Granted, you need to have the firewall turned off for this work, but there's a whole lotta machines that don't have it turned on.