When they start doing that on a mass scale, word will get out; how could it not?
And people will start lying in wait for them.
And going after those who sent them.
https://en.wikipedia.org/wiki/Fourth-generation_warfare
They won't do this on a mass scale but rather on a scale large enough to make the risk significant but small enough to not provoke an all out rebellion. The ones that get hit will have their lives utterly ruined.
And yes they can and will keep it hidden from the public. Don't believe me just know if you live in a city of any significant size the local PD and their associated SWAT teams carry out dozens of armed raids every month. Try to find out information about any of them. Try to get information on the dozens of SWAT call outs every month. Do you hear about them on the news? You may hear about one or two but for every one you hear anything about there are 50 more that you don't. You will find very quickly the police are already conducting hundreds of raids every month in total secrecy and you hear nothing about them and have absolutely no means of finding out anything or any detail. Gun confiscations will be kept even tighter. You will hear nothing about them and what you do hear will likely be disinformation.
I only bring this stuff up because people have been making the mistake of complacency for many many years. They falsely believed that if things ever got really bad there would be clear signs and people would know when and what to do. That belief was wrong then and continues to be wrong now.