Can a proxy server spoof traffic?

Question

Data protection

I use free proxies for parsing various information. Can a proxy server replace this traffic (inject software, for example)? If yes, is there a way to check this?

Answer 1

To answer the question directly: yes, it can.
BUT it is unlikely that this is still true for you.
As mentioned above, there is a difference in the protocol (http or https are the most common). In principle, you can replace anything at all, if you try hard. But it's most likely not your case.
If I understand correctly:
You are using a proxy to get or speed up access to open data.
Then the advice is simple:
Use proxies not from strange resources, do not feed configs from strange resources.
In general, everything, the rest already concerns the usual work, which is not directly related to the proxy.

Answer 2

By http maybe.
Not on https.
For parsing, keep your proxies or paid ones.

Answer 3

Maybe.
You can obviously check by comparing the response through a proxy and without a proxy.