Wa`alaykum As-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
It is permissible to work in any department in a conventional bank as long as you do not prepare any interest-based contracts or sign them on behalf of the bank.
In his response to your question, Prof. Dr. Monzer Kahf, Professor of Islamic Finance and Economics at Qatar Faculty of Islamic Studies, states:
It is permissible to work in any department in a conventional bank, credit department, the IT or software department or others, as long as you do not prepare any interest-based contracts or sign them on behalf of the bank.
This is the opinion of the greatest Shari`ah scholar of our time, the late Sheikh Mustafa Al-Zarqa (died 1999), Sheikh As-Salami of Tunisia and Sheikh Adh-Dhareer of Sudan.
The argument is that such jobs in conventional banks are not included in the wrath of Allah that is mentioned by the Prophet (peace and blessings be upon him) on the giver of riba (interest), its taker, its writer and its two witnesses (Muslim).
Besides, a prohibition of working in banks places unnecessary inconvenience and hardship on Muslims both in the Muslim majority countries and Muslim communities of other countries.
Working in conventional banks is not haram unless the worker is in the area of making loan contracts with customers.
If you are in IT job, you do not make these contracts and your work is permissible.
To claim otherwise requires evidence from Shari`ah because the Prophet (peace and blessings be upon him) declared that the wrath of Allah is on the riba’s taker, giver, writer and witnesses.
You do not have to extend this la`nah (wrath) to word processors, tellers, IT or software persons and guards of a bank.
Besides, not all conventional banks’ activities are in the area of interest; they also provide several other permissible services.
Almighty Allah knows best.