5. Basics: How to decide whether a program is safe?

Most common traits a safe program:

Must have:

1. SAFE SOURCE CODE - that you can review, alter and compile on your own. (If there is malicious lines - you can spot them and get rid of them. Open-source projects rarely have malware because they would be called out almost instantly. If something is open source it has 99.99% chance it is safe without you even checking. If it has no source code - treat it as if it were a nuclear warhead.)

The only must is be a safe open source code with no vulnerabilities.
It is enough to make a judgement always with no exception.

If yo do not want to or are unable to read code - these factors might indicate how legitimate it is:

1. COMMUNITY - People around it validate for the most part that it is safe. The more people read the code the more likely it is that vulnerabilities are eliminated.
2. RESOURCES AND FAME - Having their own website legitimizes it, having known people working on it legitimizes it, open source programs with a huge amount of contributors tend to be the best for their purpose in general.
3. POPULARITY - If safety maniacs love it - there is usually a reason for it.

That is pretty much it.

NOTE: Open source projects are mostly downloaded as binaries. Not code, but binaries. It is neat because you save on time and computing power that you have a binary ready to run but remember that someone can just put malicious code into that binary - so please compile whenever possible otherwise you are at a greater risk. There was a RAT recently found in binaries Librewolf in AUR - if you compiled it yourself you would be safe, but those who did not compile and just downloaded the binary were affected. Consider safety especially when you are a big target or when you store crypto! Crypto can be all gone suddenly, so store crypto safely or be absolutely sure you download safe stuff.

Also check types of licenses. GNU copyleft type of things are usually the nicest ones, while copyright stuff is the devil. Not always, but almost always. There are lots of types of licenses, research them if you want more details.