Which of the following security incidents is least costly to fix?

The defacing of web pages is generally considered the least costly security incident to fix for several reasons. Firstly, web page defacement usually involves altering the visual elements of a website, which can often be quickly reversed by restoring the original content from backups or through a straightforward re-upload process.

Additionally, such incidents do not typically compromise sensitive data or systems at a deep level, making the recovery process less complex and less time-consuming. Organizations may have protocols in place that allow for rapid response to these types of incidents, reducing downtime and potential revenue loss.

In contrast, the theft of program source code, corporate alteration of databases, and theft of trade secrets often involve significant resource investment in terms of forensic investigations, legal implications, and the need for system-level security enhancements to prevent future occurrences. They can lead to prolonged outages, significant revenue loss, or strategic disadvantages, thus making them much more costly to rectify compared to the relatively minor issue of web page defacement.