It doesn't need to be lethal, just highly transmissible. And persistent. Such as Herpes. And not necessarily even symptomatic.

Here's the requisite quote from Echopraxia, by Peter Watts:

> Even DNA computers, custom-built for a specific task and then tramped carelessly into wild genotypes like muddy footprints on a pristine floor. Nowadays it seemed like half the technical data on the planet were being stored genetically. Try sequencing a lung fluke and it was even money whether the base pairs you read would code for protein or the technical specs on the Denver sewer system.

More precisely, a 5 frames animation was encoded into bacterial DNA and retrieved in the genome of descendants after several generations https://www.nature.com/news/lights-camera-crispr-biologists-...

Well, a 5-frame image was already encoded into DNA about 12 months ago. [0] But this method could probably increase information density, if I'm reading it correctly.

[0] https://www.bbc.com/news/science-environment-40585299