Because worms and viruses are often spread through email, Gartner Web Development recommends multiple recipients not be placed in the ‘To:’ or ‘Cc:’ fields when emailing several people. When you place multiple recipients in the ‘To:’ or ‘Cc:’ field, all of the recipients receive the email addresses of all other recipients - as does anyone else that your message is forwarded to.

Typically, email based viruses and worms spread by scanning all files on the infected computer for email addresses. The virus then sends itself to all of the addresses that it finds. When we place multiple recipients in the ‘To:’ or ‘Cc:’ fields all of the recipients gain a larger profile to potential virus or worm exposure. Additionally, other malicious programs, including those that generate spam use a similar technique. Once an address is in a spam database, the amount of junk email that we receive in our inboxes can increase exponentially.
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