Software Updates and Why They're Important

No software is perfect. Programmers make mistakes, best practices get updated, and security problems are discovered over time.

But what happens if you don’t update your software immediately? Once a company releases a security update to fix a bug, the bug is somewhat “old news.” over time, people will be able to reverse-engineer the security update to figure out the details of the bug. These bugs are easy to learn about and cheap—or free—for adversaries to buy exploits for. They are often used in broad phishing and malware schemes to target people who have devices with out-of-date software on them.

https://www.explainxkcd.com/wiki/index.php/1328:_Update 

When you update your software, you are no longer a “target of opportunity” for cheap attacks that try to catch people running out-of-date software.

For this reason, we recommend that everybody keeps software up to date as much as possible, especially the operating system on their desktops and mobile devices. Sometimes, we run systems that are older and can no longer receive updates. Unfortunately, such devices with outdated systems are not considered fully secure anymore. If possible, it would be ideal to replace with systems which still receive updates. If this is not possible or practical, it's a good idea to still upgrade them to the absolutely latest supported version.

(content adapted from https://www.securityeducationcompanion.org/articles/software-updates-and-why-they-re-important)