Is decompilation legal?

Question

Data protection

Decompiled Android application of one large company. I wanted to see how they made one visual effect there. Looking through the code I found a vulnerability.
Unsubscribed, they fixed the vulnerability. Now they are asking how I even found it.
Should they be explained? Are my actions legal?

Answer 1

In the Russian Federation - yes, if the software belongs to you (you bought it) - no problem, do what you want.
In the US, absolutely not. "Digital Millennium Protection Act" - you can't even fix your tractor yourself, because intellectual property is on software. https://geektimes.ru/post/278644/