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Ignore them, there are tons of reasons to remove the front copyrights, here's a few:
Assists in preventing hackers from finding you via google or other search engines, as they search for such terms, XOOPS get's hackers too, don't they Damaster.
Doesn't look professional having credits pasted all over a professional website.
Doesn't look good to your client or your clients customers.
Allows your competition to compete with you easier (IE they know what your doing and how your doing it, without having to do any work themselves).
You can be ranked down in some search engines (see the whole WordPress sponsored footers thing recently).
Links could lead to offensive material when the domain name is not renewed by the developer.
Sites and software like McAfee, have a rating system, and if it leads to a red site, it could also put a mark against yours, leading to a loss of users and possibly customers.
