Ruling on working on a program that enables company clients to trade in shares

Dear Brothers & Sisters,
As-Salaamu-Alaikum wa Rahmatullahi wa Barakatuh. (May Allah's Peace, Mercy and Blessings be upon all of you)
One of our brothers/sisters has asked this question:
I was offered to work as a programmer in company of investment and dealing in the stock market, to design computer programs that make buying and selling shares easier in the market for the favour of my company’s clients. Is it permissible islamically to do this, knowing that some of the companies in the bourse are involved in haram activities, some use banks mortgages, and some are just of halal activities?
I do not or sell shares myself. I just make this process of buying and selling easier for my company’s clients. Is this considered co-operation in sin and transgression, if a client buys shares of a company involved in haram activities using my program? Or the sin is on the client himself if he does so? The company I work for told me that they do not buy or sell shares of companies whose activities are haram. Shall I accept this offer until I make sure myself if they were truthful about this or not?.
(There may be some grammatical and spelling errors in the above statement. The forum does not change anything from questions, comments and statements received from our readers for circulation in confidentiality.)
Check below answers in case you are looking for other related questions:
Working for a company that sells gold on credit
He treated the financial director and he gave him some money

Answer:
Praise be to Allaah.

If the company deals only in permissible shares, then there is nothing wrong with working on a program that enables clients to buy and sell these shares via the stock exchange. But if it deals in both haraam and permissible shares, it is not permissible to help with that, by programming or otherwise, because it comes under the heading of cooperating in sin and transgression, and Allaah 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]

Sin is not limited to the one who deals directly with the haraam thing, rather it also affects the one who helps him with that, approves of it or promotes it. 

Based on this, if you are certain that the company only deals in permissible shares, then there is nothing wrong with you accepting a job with them. 

We ask Allaah to guide you. 

And Allaah knows best.

Whatever written of Truth and benefit is only due to Allah's Assistance and Guidance, and whatever of error is of me. Allah Alone Knows Best and He is the Only Source of Strength.
Your brother and well wisher in Islam

Related Answers:
Important and precise conditions for committing an evil action by force of necessity in order to serve the interests of the Muslims
Using the company’s property for personal things
She has received a proposal from a young man who works as a producer for magazine programs on television
Working for a company that sells gold on credit
He treated the financial director and he gave him some money

Recommended answers for you:
Three questions in the grave
Why a woman should not take her husband's surname
Is it permissible to engage in coitus interruptus or to use a condom?
Ruling on democracy and elections and participating in that system
Does masturbation at night in Ramadaan invalidate the fast?