WhatsApp seems to scan my messages for personalized ads

What stops you from changing the service and suggesting same thing to your friends and family? There are alternatives around

Are you sure you didn't see any ads about backpacks before?

Smartphone chat apps are not secure. Smartphones apps are much more like web pages than desktop apps and should be treated like web pages.<p>If you have a secret to keep don’t share it with a phone.

TL&#x2F;TR: stop using WhatsApp