How can two sites exist with the exact content and not be blacklisted by google

I have just found two websites with two completely different domains but with the exact same content.
They rank very well in google too by the way.
But is this something that is possible?  I thought it was against web laws (?) to have two sites with the same content.  They are not redirecting to ONE website, they are actually 2 websites?

Can someone help me understand this please?
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Amanda WatsonWeb DeveloperAsked:
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Mal OsborneAlpha GeekCommented:
It has been observed that Google sometimes detect and penalise duplicate web content, and they have stated similar. How exactly their algorithms work, and what will actually happen in the "real world" however is unknown. Googles algorithms are secret, and change frequently; what happened last week may not this week.
Dave BaldwinFixer of ProblemsCommented:
I wouldn't be surprised if they just slipped by for the moment.  Google scans at least a billion web sites which takes a lot of time.  With that much 'work' to do, they might not get around to comparing the sites unless there was a specific reason.  What Google does look for is indications that a site is trying to scam them.  I can't tell you exactly what they would look for.

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Amanda WatsonWeb DeveloperAuthor Commented:
Its not a scam at all, its just happened to be the case and I wonder how they have been able to get away with it.  But it wasn't really  intentional
Amanda WatsonWeb DeveloperAuthor Commented:
Thanks
Dave BaldwinFixer of ProblemsCommented:
You're welcome!
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