There is a way to prevent yourself and friends against viruses and worms that spread through "e-mail address harvesting". All you do is add something to every address in your address book that makes it invalid. Here's how: Step 1: Go into the Windows Address book or where ever your e-mail address book is such as inside your mail client in Mozilla and Thunderbird's case. Step 2: Open up every entry in your address book and add in something such as "nospam" or "novirus". Every entry may look like this: email@example.com Or this: firstname.lastname@example.org Then everytime you send an e-mail to someone in the book, Edit out whatever you added. What makes this work is that e-mail harvesting worms and viruses take e-mail addresses from your address books and then it sends itself to everyone in there in the form noted down in the database. But what happens if it sends it to an invalid e-mail address? When it sends it out, The server will register an error such as "Invalid Address" and send back error messages. Those errors will probaly clog up the SMTP of the virus and proably disable it. This is a good way of protecting your friends from viruses that send itself to address book e-mail addresses.