The legal status of bitcoin (and related crypto instruments) varies substantially from state to state and is still undefined or changing in many of them. Whereas the majority of countries do not make the usage of bitcoin itself illegal, its status as money (or a commodity) varies, with differing regulatory implications.
While some states have explicitly allowed its use and trade, others have banned or restricted it. Likewise, various government agencies, departments, and courts have classified bitcoins differently. While this article provides the legal status of bitcoin, regulations and bans that apply to this cryptocurrency likely extend to similar systems as well.