We ask Allaah to reward you with good for your keenness and efforts to find out the truth, and to help your husband to find permissible employment in which there is no sin. 

Note that it is not permissible to work in riba-based banks at all, because that involves consuming riba, or writing it down, or witnessing it, or helping those who do that. 

The major scholars have issued fatwas stating that working in riba-based banks is haraam, even if the job does not involve dealing with riba as such, e.g. guards, cleaners and other services. We will quote to you some of their fatwas, whilst also pointing out that your husband’s work is strongly connected to riba and to recording and documenting it, because as you say, his main job is to ensure that all the computer systems are working correctly, and installing new systems, and assisting the bank employees. 

It says in Fataawa al-Lajnah al-Daa’imah, 15/41: 

It is not permissible for a Muslim to work in a bank that deals with riba, even if the work that the Muslim does has nothing to do with riba, because he is giving the employees who do work with riba with what they need and he is helping them with their calculation of interest. Allaah says (interpretation of the meaning): 

“but do not help one another in sin and transgression”

[al-Maa’idah 5:2]

The Standing Committee (15/38) was asked: what is the ruling on working in the existing banks? 

They replied: 

Most of the transactions that are done nowadays involve riba, which is haraam according to the Qur’aan and Sunnah and the consensus of the ummah. The Prophet (peace and blessings of Allaah be upon him) ruled that whoever helps the one who consumes riba or pays it by writing it down for him or bearing witness to it, etc, is a partner of the one who consumes it and the one who pays it, and they are all cursed and expelled from the mercy of Allaah. In Saheeh Muslim and elsewhere it is narrated that Jaabir (may Allaah be pleased with him) said: The Messenger of Allaah (peace and blessings of Allaah be upon him) cursed the one who consumes riba, the one who pays it, the one who writes it down and the two who witness it, and he said, “They are all the same.”  

Those who work in banks are helping the owners of the banks by administering their operations, whether in writing or bearing witness, or transferring papers or handing over money, or doing other things that help those who deal in riba. Hence it is known that working in an existing bank is haraam. The Muslim should avoid that and should try to earn a living in a way that Allaah has permitted; and there are many such ways. He should fear Allaah his Lord, and not expose himself to the curse of Allaah and His Messenger. 

And the Standing Committee (15/55) was asked: 

(a) Is working in banks, especially in Muslim countries, halaal or haraam?

(b) Is there any specific section of the bank that is halaal, as many think, and if that is correct could you explain further?

They replied: 

Firstly: working in banks that deal with riba is haraam, whether that is in a Muslim country or a kaafir country, because it involves cooperating in sin and transgression, which Allaah has forbidden as He says (interpretation of the meaning): 

“but do not help one another in sin and transgression”

[al-Maa’idah 5:2]

Secondly: There is no section in the riba-based bank that is exempt from this ruling according to what we know of the pure sharee’ah, because all the bank employees are cooperating in sin and transgression. 

And the Standing Committee (15/18) was asked: 

What is the ruling on working as a maintenance engineer for one of the electronics companies that deal with some of the riba-based banks, where the company sells equipment (calculators, cameras, telephones) to the bank, and tells us, as maintenance engineers, to go to the bank to service this equipment on a regular basis?  Is this work haraam on the basis that the bank does its accounts and organizes its work on these machines, and are we thus helping them in sin? 

They replied: 

It is not permissible for you to work for companies that are as you described, because that involves cooperating in sin and transgression. 

And it says in Fataawa al-Lajnah al-Daa’imah (15/48): 

It is not permissible for a Muslim to work in banks that deal with riba, because that involves helping them to engage in riba-based transactions in one way or another, by writing them down, witnessing them, guarding the bank, etc. Helping them in that manner is cooperating in sin and transgression, which Allaah forbade when He said (interpretation of the meaning): 

“but do not help one another in sin and transgression”

[al-Maa’idah 5:2]

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was asked: is it permissible to work for a riba-based organization as a driver or guard? 

He replied: 

It is not permissible to work for a riba-based organization even if you are a driver or a guard, because accepting employment with a riba-based organization implies that you approve of them, as whoever denounces something could not work to serve its interests. If he works to serve its interests, he must approve of it, and the one who approves of something haraam has a share in its sin. With regard to those who are directly involved in writing down transactions, transferring money, depositing money, etc, are undoubtedly dealing directly with something that is haraam. It was proven from the hadeeth of Jabir (may Allaah be pleased with him) that the Messenger of Allaah (peace and blessings of Allaah be upon him) cursed the one who consumes riba, the one who pays it, the one who writes it down and the two who witness it, and he said, “They are all the same.” 

From Fataawa Islamiyyah, 2/401 

And there are other well-known fatwas which forbid working in riba-based banks, no matter what the kind of work involved. Based on this, your husband has to repent to Allaah from what he has done in the past, and leave this work, seeking the help of Allaah, putting his trust in Him and being certain that He will grant him provision. Allaah says (interpretation of the meaning):

“And whosoever fears Allaah and keeps his duty to Him, He will make a way for him to get out (from every difficulty).

And He will provide him from (sources) he never could imagine. And whosoever puts his trust in Allaah, then He will suffice him. Verily, Allaah will accomplish his purpose. Indeed Allaah has set a measure for all things”

[al-Talaaq 65:2-3]

We ask Allaah to make us independent by means of that which is halaal so that we will have no need of that which is haraam.