If you are from:
- China
- Russia
- Iran
- North-Korea
- Pakistan
And some other countries, you should absolutely expect full to be under full scrutiny if you plan on working with anything related to research and development (which includes academia), infrastructure, or anything that poses a national security risk.
The cold hard truth is that (especially) those nations send operatives and assets to western countries, for the single reason of espionage and intelligence gathering. This is such a known problem that said countries tend to send their people via proxy countries.
Of course, these agencies and people are not amateurs - and blending in by the numbers is just one way to make it harder to get caught, and unfortunately means legitimate people will have a harder time to get in.