Spam comments with meaningless content?

Last time it happens very often that I comments like:
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“tabCP4 krczfsavlfay, [url=http://hdhoanbursrh.com/]hdhoanbursrh[/url], [link=http://zgyemaeehloo.com/]zgyemaeehloo[/link], http://eouyjfrkyasz.com/”
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“edPF5c eciuabehzkkp, [url=http://gprzamrrgeel.com/]gprzamrrgeel[/url], [link=http://mzpjsbcxwjxy.com/]mzpjsbcxwjxy[/link], http://dmozigjpkbbn.com/”
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all from a different IP and 20 or 30 in a row. Why does someone or make a software program post content like this? its totally useless because the homepage URL etc is just gibberish.
I think I have to put in CAPTCHA.