I hear there's an e-mail message making the rounds that can trash my hard disk when I open it. Is this true?

Do not believe in hoaxes... Use a good antivirus system with an active subscription, keep your antivirus databases updated to the latest and forget the rest... leave the job of being able to track the virus to the antivirus system.  After all, the antivirus company has a reputation to maintain. :-)

On a generic basis, do not open email that look suspicious or have come through unknown sources... with the large number of emails coming in nowadays, I am sure it is not very difficult to distinguish the right ones from the wrong ones... 

For many years the answer to this question was a resounding no and that is largely the case now as well. There are a series of hoax chain letters that are seemingly endlessly circulating around the globe. A typical letter is the "Good Times" hoax. It will warn you that if you see an e-mail with a subject line that contains the phrase "Good Times" you should delete it immediately because the very fact of opening it will activate a virus that will do damage to your hard disk. The letter will encourage you to send this warning to your friends.

The "Good Times" hoax, and many like it, are simply not true. However there are enough people who believe these hoaxes that the messages are endlessly forwarded and reforwarded. If you get a letter like this one, simply delete it. Do not forward it to your friends, and please do not forward it to any mailing lists. If you are uncertain whether the letter is a hoax, refer it to your system administrator or network security officer.

Just to make life complicated, however, there are some cases in which the simple act of opening an e-mail message can damage your system. The newer generation of e-mail readers, including the one built into Netscape Communicator, Microsoft Outlook Express, and Qualcomm Eudora all allow e-mail attachments to contain "active content" such as ActiveX controls or JavaScript programs. As explained in the JavaScript and in the  ActiveX sections,  active content provides a variety of backdoors that can violate your privacy or perhaps inflict more serious harm. Until the various problems are shaken out of JavaScript and ActiveX, enclosures that might contain active content should be opened cautiously. This includes HTML pages and links to HTML pages. Disabling JavaScript and ActiveX will immunize you to potential problems.