The group of microorganisms you are describing is called viruses.

Here's why:

* Hereditary material: Viruses contain either DNA or RNA as their genetic material.

* Protein covering: This is called a capsid, which protects the genetic material and helps the virus attach to and infect host cells.

Viruses are considered obligate intracellular parasites, meaning they need a host cell to reproduce. They cannot replicate on their own.

Let me know if you have any other questions about viruses!