Keep your operating system, installed programs or mobile apps updated. Hackers often penetrate exploiting a vulnerability that exists in software. You probably heard of WannaCry, the ransomware attack that occurred in May 2017. WannaCry spread by exploiting a vulnerability in Windows and the impact was global. Microsoft had released patches before the attack, yet many organizations had to apply those.
When a vulnerability is discovered, the developer company often provides fixes for those security holes in updates. Moreover, many such security holes in popular software are often available on the internet. Running outdated software is like keeping a door open for the criminals.