Typo Domain Names

Registering typo domains (provided they are not trademarked) could be seen as unethical.

While there is no "internet law", it may not be illegal in your part of the world. However, if you register a typo domain and then divert traffic (ads, affiliates etc..) to the real company, then that practice may land you in court. Such action could be performed in conjunction with a UDRP (Uniform Domain-Name Dispute-Resolution Policy).