Email systems at thousands of companies' offices around the world were attacked by a virus called "Mellissa" that  _ itself as "an important message" from a friend. "Even though there was a weekend warning, more than 50,000 companies at about 100 places around the world have been attacked by the virus," computer experts said on Monday. The virus began to show up last Friday and spread rapidly the next first workday by making computers send off dozens of email containing the virus. Although the virus had no long-lasting damage to a computer, its effects were far-reaching. Michael Vatis, a senior US official said military and government computers were damaged, along with thousands of the other instructions' systems. The body of email message says "Here is what you ask for..." Once the user opens it, the virus digs into the user's address book and sends out messages to the first 50 addresses. The reason the virus spreads so rapidly is that you're getting it from people you know and trust. So anyone who gets an unexpected email with the "Important Message" subject line is advised not to open it and to delete  it immediately. The virus spreads rapidly because  _
it makes computers work without stop it carries words "Important Message" it sends out messages to dozens of people who know and trust the sender at one time it attacks military and government offices