Why do some websites say not secure in Safari?

Related questions

1. What are extensions in Safari?
2. Can I uninstall Safari?
3. Is Safari browser any good?
4. Why is my connection not private?
5. How do I get rid of Safari extensions?
6. Why is my website insecure?
7. Where is the extensions button on safari?
8. Is Safari browser safe?
9. How do I get rid of unwanted extensions?
10. Why do websites say not secure?

Tags

1. #meaning
2. #connection
3. #encrypted
4. #warning
5. #visiting
6. #safari
7. #insecure
8. #encryption
9. #secure
10. #https
11. #message
12. #address
13. #indicating
14. #websites
15. #iphone