Is the income earned from a computer maintenance company, most of whose clients deal with hotels and stock exchanges, permissible (halal) or forbidden (haram), especially given the presence of women in places of work, such as hotels, who do not observe modest dress?

If computer maintenance does not involve assisting in something forbidden, then there is no objection to it, provided one lowers their gaze and avoids unlawful seclusion. The criterion is whether the work assists in something forbidden or not, either with certainty or strong probability. Since the predominant nature of stock markets and hotels nowadays involves trading in both permissible and impermissible stocks and bonds, and the condoning of alcohol and nudity, any part of your work connected to these matters is impermissible, due to Allah’s saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." Funds acquired from impermissible work must be disposed of by spending them on the welfare of Muslims. In the future, it is forbidden to assist in any forbidden act, and if one cannot continue in the work without doing so, it becomes obligatory to leave it.