That article gives a ton of good reasons to flat out refuse to talk about anything of substance to any agent, ever, without your attorney present.
I would highly recommend reading it. Even if you don't think you're personally the target of an investigation, the way these things go, anyone that they can catch in the net is a potential target, so you should be nervous - it always looks better to indict N+1 people than N, and if you talk to the investigators at all without a lawyer present, you greatly increase your chances of being that +1, even if you truly and honestly haven't done anything wrong.
I would highly recommend reading it. Even if you don't think you're personally the target of an investigation, the way these things go, anyone that they can catch in the net is a potential target, so you should be nervous - it always looks better to indict N+1 people than N, and if you talk to the investigators at all without a lawyer present, you greatly increase your chances of being that +1, even if you truly and honestly haven't done anything wrong.