Viruses and prions are not alive. They are codes written in amino acids and assembled into programs call proteins. Like the biological viruses responsible for human disease these viruses can replicate themselves in minds but they need to "hijack the machinery of life to do
it. These are ideas, or complexs of ideas attractive to us. The poisonous information or virus is parasitically dependent on living thing to spread it through mind space, the undead thing home. Neal Stephenson described them in SNOWCRASH the undead things inject themselves into living things but they themselves are not alive.
Just as their are simple undead things in biology like prions and viruses, their are more complex undead parasitic entities which can not reproduce themselves and do "high jack the machinery of life" Do not imagine this happens only in biological organism at the microscopic scale. Nature repeats up and down the magnitude across species.