another possibilty!
If you bought some gambling websites with content -and worse used it for other sites you own- it will sometimes be impossible to check if it is all original!
So the best thing you can do is to put an emailaddress on your website so a webmaster can contact you in case you might be in a violation.
Not all websites seem to have a valid emailaddress though!
Second, cooperate and pull off duplicate content asap.
Rick