So, if he’s in the EU, he can do it. (IANAL, but this was the conclusio of an EUGH decision). Otherwise it gets harder.
(I can’t find the ruling right now either)
Two companies were involved, company A and company B. Company A developed an office suite containing a macro language, company B developed their own office suite and wanted to have compatibility to the macro language of company A’s suite.
So company B decompiled company A’s suite, copied the decompiled code of their APIs and built their own interpreter.
The court ruled that while source code itself is a copyrightable creative work, compiling and decompiling it produces code that is not directly related anymore, and, while it is based on the original code, the only similarities between both types of code are that they describe the same algorithms. But, per european law, algorithms are not copyrightable, only patentable, so the result of a decompilation step is not directly copyrighted work.
Additionally they argued that in other industries, like automobiles, it is common to take apart the products of your competitors, analyze them, and use the knowledge gained for your own products (unless you infringe patents, of course).
And this basic right to own stuff also gives you the right to take apart stuff you have a license to use under the condition that it does not provide a direct loss for the person selling you the license, for example you can not take apart a rented car, but you can take apart a car you bought.
Additionally the court argued that this right can not be signed away, not even in private contracts or through ToS or EULAs, as it would severely restrict the right to "own" stuff.
IANAL, this is not legal advice, consult a lawyer (or rather several, this topic is complex) if you intend to use this as defense in court.
'Hola built a peer to peer overlay network for HTTP, which securely routes the sites you choose through other Hola users' devices and not through expensive servers'.
so it is a p2p system...