It's been fully 20 years, I believe, since it is claimed that Russian scientists were able to replicate by constructing from elemental molecules, the complete structure of the smallpox virus.

Evidence is not conclusive, but is very persuasive, that this was actually done with the results claimed. (Reported in some detail in Technology Review, but it's been too long ago for me to have citations handy.)

There have been several claims of similar "built-from-ground-up" simple viral and protviral structures having biological (infectious) capabilities. Such claims seldom are contested, since serious researchers consider them more in the category of "parlor magic" than as having serious potential - in the absence of any intent to use them maliciously.

On researcher claims to have been "back-tracking" viral infections that appear to have infected ancestors during our (and other related creatures') evolution, using DNA changes that were quite probably caused by them, and has had some success in reconstructing viral agents that no longer exist, but that may have had sufficient effect on once-living ancestors to have altered our own DNA and that of other closely related creatures. ... ... ...

John