According to an excellent article by Elinor Mills on ZDNet‘s blog:
“the fake alert informs recipients that as part of a “State Vaccination H1N1 Program” they need to create a profile on the CDC Web site. The link in the e-mail goes to a fake CDC page where the visitor is assigned a temporary ID and a link to a vaccination profile that is actually an executable file containing a copy of the Kryptik Trojan targeting Windows, according to an AppRiver blog post on Tuesday. Once installed, “this Trojan will create a security-free gateway on your system and will proceed to download and install additional malware without your authorization,” the post warns. “It also enables a remote hacker to take complete control of your computer.” You can link to the full article here.