What's true:

* Sterile environment is free of actively growing cells and microorganisms: This is the fundamental definition of sterility. It means that there are no living organisms capable of multiplying in the environment.

* May contain viruses: Viruses are not considered living organisms in the traditional sense. They lack the machinery to replicate on their own and require a host cell. Therefore, a sterile environment may still contain viruses, but these viruses cannot reproduce without a host.

* May contain dormant life forms like endospores: Endospores are highly resistant structures formed by some bacteria, like Bacillus and Clostridium. They are incredibly resilient to heat, chemicals, and radiation, allowing them to survive in harsh environments. While a sterile environment would kill any actively growing bacteria, it might not eliminate all endospores.

What's important to remember:

* Sterilization methods: Different methods of sterilization have varying levels of effectiveness against different microbes. Some methods, like autoclaving, are highly effective at killing endospores, while others, like filtering, might not be.

* Dormant life forms can become active: Endospores can remain dormant for years, but they can re-activate under suitable conditions, potentially contaminating a previously sterile environment.

In conclusion:

While a sterile environment is free of actively growing cells and microorganisms, it might still contain viruses or dormant life forms like endospores. This doesn't mean the environment is truly "safe" in all contexts, as dormant forms can reactivate. The actual level of contamination and potential risks need to be considered based on the specific context and the sterilization method used.