How does hypochlorous acid inactivate viruses?
The other answer by @CMosychuk talks about the general aspect related to use of hypochlorous acid. I will discuss here its molecular mechanism of action.

Hypochlorous acid (HOCl) is a very powerful oxidizing agent. In aqueous solution, it dissociates into H+ and OCl- as:

$$\ce{HOCl \leftrightharpoons H^+ + OCl^-}$$

However, HOCl also destroys viruses by chlorination. It acts on anything, from lipids to nucleic acids. For example, Hawkins et al ,2002 describe in detail the effects of HOCl on nucleic acids. HOCl, by direct chlorination, leads to the formation of chloramines, and ultimately nitrogen-centered radicals. These radicals often react with each other to form dimers. Also, they have reported formation of single- as well as double-stranded breaks on application of HOCl on plasmid DNA. See this image:



These reactions render the nucleic acid useless and the virus harmless. In a similar manner, HOCl also reacts with polypeptides, ultimately leading to their fragmentation. See these images (from here):





Also, as mentioned in the other answer, application of HOCl has been shown to promote denaturation and aggregation of proteins. The linked paper also talks about HOCl's effects on other biomolecules, such as carbohydrates, but those effects would be out of scope here.