There is a new strain of the Sober virus roaming inboxes lately. Yahoo has more. The virus arrives in an email with an attachment. Many of the messages will proclaim they are from the CIA or FBI asking you to open the attachment to answer some questions. Some attachments claim to be video of Paris Hilton or Nicole Richie. In short don't open the attachments.
...Add this to the long line of virus that are avoided if you just don't open attachments or view email from people you don't know. By this time everyone who owns a computer and gets email via Outlook or some other mail client should be running antivirus software. A huge benefit of using web based email services like Hotmail is that most provide server side virus scanning on attachments before you download them. If you connect via POP3 or IMAP to Hotmail or Yahoo! or *Mail then you are responsible for scanning mail and attachments with your personal antivirus software.