Recently the SEC decided that they have jurisdiction of international blockchains on decentralized networks.
What this boils down to, is tokens like the DAO are considered securities within the USA. What this means is that exchanges that operate in the USA, such as Poloniex, Bittrex, or Coinbase will not be able to carry such tokens in the future.
Offering public securities for sale in the USA which are not registered by the SEC is illegal. Accredited investors in the US, are people who have net worth above $1 million dollars and they will be the only people legally permitted in the US to invest in start-ups such as the DAO which sell securities.
The difference between a cryptocurrency and a security are nuanced. The SEC did seem to recognize in their report that Ethereum was a currency and not a security.
Tai made a video covering this issue with an experienced lawyer, this is worth a watch if you are an investor or if you do blockchain projects:
Even people outside the US can fall into legal trouble, from what I know. If businesses or enterprises outside the US, market their securities to US citizens in any way, charges could be pressed in the future, and I am not an expert, but many countries have extradition agreements with the US. It is certainly something to look at if your security can be sold to US investors.
The wonderful thing about the Ethereum blockchain is, all of its ICO's and token issuances can be sold to US investors. There is no way to limit that on a blockchain. Interestingly, the SEC does not care about code. They focused largely on marketing materials associated with the DAO rather than what the code said it was.
Their full report is here: https://www.sec.gov/litigation/investreport/34-81207.pdf
A token like TenX is probably also classified as a security, just in my limited understanding of the Howey Test.
Good thing I prefer currencies and not tokens. Tokens will generally be limited by the same limitations that face stocks. Currencies can trade into the multi-billions without any issues.