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When presenting from your slide deck, any slides with inserted web pages will display a security bar at the bottom. This will tell you if the site is secure or not. If you select the security icon the bar will expand providing you with more information.
The blue circle and exclamation point inside indicates a secure website. Information provided to this site will be kept private.
The red triangle and exclamation point tells you the site is insecure. It would not be safe to provide any kind of sensitive information to this site.