Basically we don't know the risk in every site if you invest money in a site first is you don't know if the site was trusted there are site that can give you small profit but many site are just scamming people who invested.
Yes, and every investments has a risk specially bitcoins since it is crypotcurrency and mostly all its transactions are internet based then that would also be vulnerable to all threats via internet and same goes with all risks in common marketing investments though I would say bitcoin has the highest potential for earning among other investments options now. So it compensates the risks compared to all your possible earnings.