It seems that the FBI has concluded correctly that Bruce Ivins was a lone nut who mailed the anthrax letters in September and October 2001.

Nevertheless, we still might have a continuing reliability problem within our organizations that research biological and chemical weapons. After the FBI caught and prosecuted the Rosenberg ring in our nuclear-weapons program in the early 1950s, we continued to learn intermittently through the next five decades that there had been many individuals inside the program giving information to the Soviet Union.

I don’t think the main problem is inside people who ideologically support Al Qaeda, although there apparently was at least one of those:

http://www.rantburg.com/poparticle.php?ID=241852&D=2008-06-16

Rather, the more common problems are inside people who feel they need money so desparately that they will sell their secret knowledge, inside people who have become profoundly contemptuous of our country’s institutions, and inside people whose personal lives have become so troubled that they concoct bizarre, grandiose schemes to redeem themselves. In brief, we might have quite a few inside people who are grossly unreliable but who have access to knowledge and materials that can enable mass murders on the scale of tens of thousands of people.

I think we probably are safe for a while, but after our current vigilance ebbs in a few years, there might be foreigners with a lot of money traveling around trying and managing to buy such knowledge and materials.