The ruling on studying networking for one who will use it for haraam purposes

There is nothing wrong with teaching networking, even to non-Muslims, because it has numerous uses and is not usually used for haraam purposes, unless you know — or think it most likely — that the student is only learning it in order to use it for haraam purposes, or that this is usually the case for those who study that in that country. In that case, it is not permissible to teach it, because that is spreading corruption and helping in sin and transgression. 

The basic principle to be followed in this matter is that it is not permissible to be hired to do something haraam or to do something that may lead to haraam, because when Islam forbids something it blocks the means that lead to it. 

Allah says (interpretation of the meaning):

“Help you one another in Al‑Birr and At‑Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression. And fear Allaah. Verily, Allaah is Severe in punishment”

[al-Maa’idah 5:2]

Shaykh ‘Abd al-Rahmaan al-Sa‘di (may Allah have mercy on him) said: With regard to every sin and wrong action, a person must refrain from it himself, then he must help others to refrain from it.

End quote from Tafseer al-Sa‘di, p. 218. 

Imam al-Shawkaani (may Allah have mercy on him) said:

Everything that a benefit depends on is permitted by sharee‘ah: so selling it is permissible. And everything that has no benefit at all, or that benefit is not permissible, then selling it is not permissible, because the means that leads to haraam is also haraam. But it is essential that the benefit in that thing should not be haraam in all cases. 

But if it is something of which the benefit may be halaal in one case and haraam in another case, or it is something that may be used in a haraam way or in a halaal way, if the seller knows that that purchaser will only use it for haraam purposes, it is not permissible to sell it to him; but if he knows that he will use it for halaal purposes, it is permissible to sell it to him. If the matter is unclear and it is possible to use it in both halaal and haraam ways, then it is permissible to sell it, because there is no impediment to selling it, and uncertainty without knowing what is more likely to be the case is not to be paid attention to. 

Then he said, after mentioning the evidence for what he stated: 

To sum up, if it seems most likely that it will be used in ways that are not allowed, which is the haraam benefit, it is not permissible to sell it. The fact that it is most likely to be used in a haraam way should make the seller think that the purchaser is only buying that item for that haraam usage. But if that is not the case, then the matter is as stated above. 

An example of that is selling grapes and dates to one who it is thought most likely will use them to make khamr, or selling musical instruments, which are only used for haraam purposes. In that case it is not permissible to sell them, because that usage is haraam, and whatever it haraam, it is haraam to sell it. End quote. 

Al-Sayl al-Jaraar, 1/485-486 

See also question no. 105325 and 125779 

If someone learns this knowledge from you and you do not know what he will use it for, or he appears outwardly sound, then he uses it for something haraam, such as setting up a network for a pub or bar, or riba-based transactions, his sin is on him and you will not be affected by his sin. 

And Allah knows best.