An electronic chain letter is an email that urges you to forward copies to other people.

Chain letters, like virus hoaxes, depend on you, rather than on computer code, to propagate themselves. The main types are:

• Hoaxes about terrorist attacks, premium-rate phone line scams, thefts from ATMs and so forth.
• False claims that companies are offering free flights, free mobile phones, or cash rewards if you forward email.
• Messages, which purport to be from agencies like the CIA and FBI, warning about dangerous criminals in your area. 
• Petitions. Even if genuine, they continue to circulate long after their expiry date. 
• Jokes and pranks, e.g. the claim that the internet would be closed for maintenance on 1 April.

Chain letters don’t threaten your security, but they can waste time, spread misinformation and distract users from genuine email. They can also create unnecessary email traffic and slow down mail servers. In some cases the chain letter encourages people to send email to certain ddresses, so that these are deluged with unsolicited mail.

The solution to the chain letter problem is simple: don’t forward such mail.