Sometimes a hyphen is actually part of a business name, such as in "Harley-Davidson." However, they have both Harley-Davidson.com and HarleyDavidson.com. The latter forwards to their hyphenated name. So, unless the hyphen is integral, I recommend avoid using it.

If a hyphen is used because the preferred domain name is already taken, it is more apt to be confused. Also, I suggest registering hyphenated domains and other similar domains, if the unhyphenated version is already owned to prevent copycats that intentionally try to obfuscate.

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