"However, the Senate Judiciary Subcommittee on Immigration and the National Interest used publicly available information and identified at least 17 individuals from these seven nations that from March 2014 to June 2016 were implicated in terrorism.
Wow, 17 whole people from 7 different nations.
How about this then:
http://researchbriefings.files.parliament.uk/documents/CBP-7613/CBP-7613.pdf
In Great Britain, between 11 September 2001 and 31 December 2015, 656 individuals were prosecuted for terrorist offences, 542 of whom were convicted.
That's a mean of roughly 38 a year, from one country.
So maybe the UK should be added to the immigration ban as well?