Chain Letters Are Some Sort of Cyber Attack
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I really dislike those messages on WhatsApp with the label
"forwarded many times". Most of them simply suck. I want it to stop.
Some people forward them and when you point out that the chain letter
is irrelevant, they find reasons to post them just the same. Last one I saw is 
about people knocking on your door impersonating employees of the Ministry of 
Interior. 
Back in the days I was on Facebook, I've found a solution to those
chain letters: threats to unfriend those who forward them. Now, I'm not on 
Facebook, but I still use WhatsApp because if you want to be part of 
communities, that's the way to communicate.

Other well known chain letter is that pyramid scam found on internet
forums offering you money if you duplicate the message and send money 
to the dude at the top of the list. You are more likely to get a letter
reading "Do you expect to find money in this envelope, you moron?".

Now, when one forwards a chain letter he or she adds to traffic on
the web. The messages are save to disks. Servers are processing more
requests, and generate heat. The servers use water cooling. 

Now, if you see an internet forum filled with chain letters, that's
a problem. And if you forward them, you act like a human bot.
That's why though they don't steal your personal data, and don't 
jarm your computer, they are some sort of cyber attack.