The Storm Worm is a backdoor Trojan horse that affects computers using Microsoft operating systems. The worm is also known as:

Small.dam or Trojan-Downloader.Win32.Small.dam (F-Secure)
CME-711 (MITRE)
W32/Nuwar@MM and Downloader-BAI (specific variant) (McAfee)
Troj/Dorf and Mal/Dorf (Sophos)
Trojan.DL.Tibs.Gen!Pac13[3]
Trojan.Downloader-647
Trojan.Peacomm (Symantec)
TROJ_SMALL.EDW (Trend Micro)
Win32/Nuwar (ESET)
Win32/Nuwar.N@MM!CME-711 (Windows Live OneCare)
W32/Zhelatin (F-Secure and Kaspersky)
Trojan.Peed, Trojan.Tibs (BitDefender)

As of late, it has been passing itself off as an email message that someone has sent you an ecard, or some variation of that.

Don't be fooled!