Is it permissible to work on repairing software for a company whose owner deceives customers by selling defective programs? Is it permissible to create a new program for a client of this company, independently of its owner? And is it permissible to offer work to the company's clients and explain the defects in its programs?

You should advise the company owner and those who assist him to fear Allah and repent from the act of deception and ill-gotten gains. It is not permissible for you to remain silent about this evil or participate in it. Correcting faulty programs is permissible. If the company owner does not desist from his deception, and you are unable to condemn him and expose the flaws to people, then do not attend the gathering of deceit and forgery, and seek another job. It is not permissible to use company funds to develop programs without the owner's permission, nor is it permissible to work for your personal benefit during official working hours. However, outside of official hours, there is no harm in doing so. Warning the company's customers about the ongoing deception is required. It is not permissible to betray the company owner or use his money without his permission. If the company owner asks you to cheat in a program, do not do it, and implement what was agreed upon correctly and soundly without informing him.