Question: *[Blindsight](https://en.wikipedia.org/wiki/Blindsight_(Watts_novel))* mentions a group of 5 transhumans in a first contact with an unconscious alien species (Rorschach).

Which the writer mentions any form of communication in human language, interpreted by the species is treated as an attack. But how?

From the book:

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> "Since Rorschach doesn’t have consciousness, human languages and signals are meaningless to it. The act of receiving and decoding the signals consumes time and energy but yield no benefit for Rorschach. Thus, for Rorschach, human language is virus, and “communication” in human language is an attack.
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> "Imagine that you encounter a signal. It is structured, and dense with information. It meets all the criteria of an intelligent transmission. Evolution and experience offer a variety of paths to follow, branch-points in the flowcharts that handle such input.
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> There are no meaningful translations for these terms. They are needlessly recursive. They contain no usable intelligence, yet they are structured intelligently; there is no chance they could have arisen by chance. The only explanation is that something has coded nonsense in a way that poses as a useful message; only after wasting time and effort does the deception becomes apparent. The signal functions to consume the resources of a recipient for zero payoff and reduced fitness. The signal is a virus. Viruses do not arise from kin, symbionts, or other allies. The signal is an attack."
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The writing is quite dense and could anyone explains whats the reasoning behind human language being hostile when interpreted by the Rorschach?

Answer: 
I think a real world example of this would be a DDOS attack on a website. Malicious users flood the website with, more-or-less, nonsense signals. This takes up all the website's ability to interpret any sort of incoming information. If someone watching the website notices a bunch of nonsense signals hitting the site, they could assume it was an attack on the site. 

So the Rorschach species might interpret the nonsense communications similarly as a malicious attack.
It looks like you're asking for an interpretation of this passage from the book.

The key point, is that Rorschach has *assigned a motive* to the communication. Since it cannot interpret the message, it can only suppose that the message *has* no meaning; it has categorized the message as nonsense, and furthermore categorized it as *deliberate* nonsense. It's as if it's thinking "Why else would something communicate a message with no meaning? It must be on purpose!" Since attempting to interpret the message consumes energy, Rorschach views the communication as ethically equivalent to trying to suffocate it to death with a pillow. This may not be what the transhumans intended, but no other interpretation has occurred to Rorschach, so it takes it as an attack.