There's no evidence that a doomsday virus can be created. There's a tradeoff between how infectious and how deadly a disease is. You would have to develop a two-stage virus, and that would require a large lab or labs with material being shipped there. Something humans would definitely notice. Even then, how would the virus reach literally everyone? People will take measures to not become infected once the threat has been identified, and some people and groups are isolated as it is. And no virus kills everyone. Rabies comes closest at 99%. But unlike what the zombie genre would have you believe, it has a poor means of delivery.

This isn't like vibe coding. The AI would have to make the virus in laboratory conditions and then disseminate it globally without prior detection.

I believe the main fear is bioterrorism

You don’t need to attack humans directly. Simply making and distributing a virus or fungus that successfully damages the grasses that we use for the bulk of our calories would do the job.

You'd need to hit wheat, corn AND rice at the same time. And we probably have 10 others we're not using because those 3 are already enough. It would be a tragedy but we can eat lots of things.

They are very closely related and share a number of fungal pathogens. In addition as grown they are almost a small set of monocultures.

"Simply"? You might as well say the same thing about creating a doomsday virus.

Yes, with AI I will be able to simply build a doomsday machine. Claude will just tell me how to build a supply chain, circumvent regulations and do this without anyone finding out.