If you overhear someone talking about an impending acquisition in a coffee shop, and you trade on that information, you're quite safe in the US. European countries can and do consider that insider trading, though.
If you manage to discover confidential data in a way that does not compromise such an agreement or duty, you're fine. Obviously you should engage with an attorney instead of taking legal advice from a random HN comment, but there's really no issue with this. Information asymmetry is a fundamental part of the market and not illegal on its own.
Source: I used to work in financial forecasting using significant amounts of alternative data.
As long as I didn't _take_ that info from anyone (e.g. I can't hack emails, or bribe an accountant, etc. etc.), this is markets behaving exactly as we want them to.
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