Generally speaking, at least as far as the US, companies that are in different industries can share the same name. For example, ABC Pens and ABC Widgets. However, in the case of companies that may be considered household names like Microsoft, Xerox, etc., you might run into problems using the same name.

As far as the domain name, when you have a domain that is the company's own name, you can run into search problems because branded searches will return both companies. Since users typically click the first result, the larger established company is likely to get the bulk of clicks unless it is immediately obvious that that is the wrong company, and the customer knows that there are two companies with that name.

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