Yup: It's legit, all right; here's the skinny from the SYMTECH (NORTON) Site:
W32.Navidad Discovered on: November 3, 2000 Last Updated on: November 11, 2000 0 9:38:15 PM PST

W32.Navidad is a mass mailing worm program. The worm replies using MAPI to all Inbox messages that contain a single attachment. This works with Microsoft Outlook. The worm utilizes the existing email subject line and body and attaches itself as NAVIDAD.EXE. Due to the bugs in the code, after being executed, the worm causes your system to be unusable.
It is listed on top of their highest risk list, but a "fix" and update is available. Apparantly, as with many of these E-mail Worms, MS Outlook Express is particularly vunerable. For what it's worth, a Tech Support type advised that EUDORA E-mail server is essentially immune to these boogers, as it does not use MS protocols, or something... I got a "lite" trial version, and it's OK.