“Operating systems lacking the latest updates put you at risk, because they have a lot of known vulnerabilities,” says security professional John Opdenakker.
He advises people to “always install the latest updates.”
If your phone is running a really old version of your operating system, and a new one is available, it’s a good idea to update it now. You’ll then be able to use WhatsApp again straight away.

What if my phone can’t run a newer operating system?

Of course, some iPhone and Android phones will not be compatible with newer operating system versions. In this case, the first choice if it’s available to you, would be to upgrade your phone now. 
“When you can no longer update the operating system and apps on your device, the only solution is to buy a new phone,” Opdenakker says. “When you do so, it is important to check for how long, and how often, updates are released by the vendor.” 
This might not be an option for you, but it should be noted that if you remain on an old operating system, your phone is not as secure as it should be.

WhatsApp security

WhatsApp is a huge app, with half  a billiousers, so it’s no surprise that it is often targeted by hackers. Therefore, to remain as secure as possible, it makes sense to always ensure you are running the latest version.

WhatsApp alternatives

WhatsApp is probably used by most of your friends and family, so it’s hard to break away and try another app. However, WhatsApp is owned by Facebook, which has already put many people off, , especially as back end inegration is currently ongoing.
There are several alternatives you can try, including Signal or Wickr, that could make your communications more secure. At least try them out for size, and see if you can persuade others to get on board too.