It was expected, bitcoin technology, opened the way to the cryptos but it is obsolete, and more time more possible attacks or vulnerabilities will appear, for that reason coins like IOTA, I consider that they are great initiatives and it is an advance in the correct direction, despite the problems that is presenting in the last months.

I do not know about the attack of 51% thanks to @dragosroua, it is something that I will take into consideration, now that I am venturing into the world of cryptos.