In the flurry of more than twenty security updates which Microsoft
released last week, it was easy to overlook one particularly insidious
hole: a flaw in SMTP affecting Windows XP, Windows Server, and Exchange
Server. There are probably a few computers out there running one or the
other of these systems.

SMTP stands for “Simple Mail Transfer Protocol,” and is one of the
standard components used by most operating systems through which
computers talk to each other during the sending and receiving of e-mail.
As you might imagine, it’s ubiquitous in its deployment.

And no little flaw, this. Rather a great big hole you could drive the
proverbial Mack truck through. [...]