What are the squigly letters and numbers for?

After you complete certain pages on yahoo (to join a group for example) it asks you to type in the characters you see in this box at the bottom of the page. The letters and numbers are always ';squigly'; looking and turned in various directions. What is the purpose of this?What are the squigly letters and numbers for?
The purpose of those ';squigly'; characters that you are sometimes required to type in, is simply to ensure that a human is performing that particular task and not a computer. It helps to prevent spamming of sites with a large number of requests, as a computer might be able to handle, but not a human.What are the squigly letters and numbers for?
That is so only a HUMAN can clearly read them and type them in. It is a security device to stop spammers and ';automatic sign-up'; trolls, etc.
I don't know LOL it is really silly.
It helps prevent unauthorized use. Malicious people can set up computer programs that can look for words in boxes, but they have a harder time seeing those warped pictures.
They TELL you the purpose. It's to make sure you are the person signing up for whatever it is. If you were at a totally strange computer, you probably wouldn't be able to read the squiggly letters.
They're for sh-its and giggles.

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