5 cents
Sounds like a hoax.
If it is not, I would think that you are probably in one of the 'sensitive technology' fields. Are you involved in any research remotely related to defense or potentially with a 'dual use' background ?
If it turns out not to be a hoax:
1. get a good lawyer.
2. fire that one, get a better one.
3. try to meet them on your turf, your companies office, your attorneys office, not your apartment.
4. try to remember
- what student organizations you belonged to,
- whether you ever sat next to someone who in this post 9/11 paranoia now might seem suspicious.
- try to rember all contacts to your home goverment you ever had.
5. don't keep any documents related to your work at home. Copy your personal files from your pc onto a CD. Get rid of the PC, preferably by a process involving temperatures above 1400C.
The goverment doesn't make housecalls because they like you or bc they want to 'chat' about your illustrious training background. They are up to something, and I am afraid it is nothing good.
Anybody remembers that chinese scientist at one of the national laboratories ? In the initial reports the goverment made it look like he sold the bomb to the soviets, after a lenghty investigation they could barely cite him for jaywalking.
(And beware of friendly people)