Security through obscurity (STO) is reliance upon secrecy in software development to minimize the chance that weaknesses may be detected and targeted.
Security through obscurity is often achieved by developing code in secret, protecting it from unauthorized access and maintaining the software’s proprietary closed source status. The approach can be effective in combination with other measures but STO on its own is deprecated. Used to bolster more effective approaches such as security by design, security through obscurity can add another layer of protection.
Security through minority is a subcategory of STO that is based on code that is infrequently used. That approach relies on the knowledge that hackers looking for vulnerabilities to exploit typically seek commonly-used software to maximize sales of malware and hacking scripts and increase the number of computers they can reach.
Similarly, security through obsolescence relies on the fact that programs that are no longer used are less likely to be exploited because few are familiar with coding for them-- let alone exploiting their code.
Security through diversity can also be effective. This approach involves using a combination of piecemeal components. Security through diversity can make a system harder to target and can be inherently more secure than a well-known monolithic solution.