I totally disagree with this decision SEC always took action very late against big ICOs why not they awake on the right time and now again people will lost their money without getting any refund. This is really unprofessional behavior what happening in this case because SEC has fishy track record.
Before Telegram started their private sale, SEC had long hinted that they will go after crypto crowdfundings. That is why you see many ICOs before barring US citizens from participating in their token sale. Telegram knew that and the risk involve but they still took it. I'm not saying what the SEC is doing is good either, they probably targeted telegram because of that huge money coming from US investors.
Yes the SEC could have easily made a decision a very long time ago but for them to do it at the 11th hour to a project that raised $1.7 billion is beyond a monumental PR failure for both Telegram and the SEC.
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It probably took them time to figure that out but who knows? It could also be their strategy to kill telegram for whatever reason.