Although a trademark is protected, however it may be vulnerable overseas. Before the Internet, that may not have mattered so much. Today, however, someone in another country using an already protected trademark could be as damaging as someone opening store with the same name as yours in your domicile.
Trademarks rights are territorial, meaning that they are only granted on a country-by-country basis. Trademark registration in one country does not protect a trademark in a foreign country. Trademarks are territorial and must be filed in each country where protection is sought.
Furthermore, in most countries, the only way to acquire recognized trademark rights is only by way of registration, which is often given to the first applicant regardless of the applicant’s (or any other company’s) commercial use of the mark.
Even if you are using your brand name for your business and if you did not register your trademark early enough, someone else can lawfully own the trademark in a country.