Your digital footprint follows you where ever you go. A digital footprint is everything you have ever done of the internet or and text message you have ever sent. To have a digital footprint, you must first become a digital citizen. Once you have became a digital citizen you will now have a digital footprint.
The grandma rule is telling you to never put anything on the internet that you wouldn't your grandma to see. Once you put something on the internet, you can't erase it, because what's on the internet, stays on the internet forever. The rule applies to text messages to. If you send a text to someone, you better think twice about what that text says.
Viruses and Malware
A virus is something that you can get on your computer and make it run slow. Malware can also make your computer run slow. If you ever go to a web site or get a pop-up add that says you won a million dollares and it gives you a link to go to, you should never click on it. Most likely it will carry a virus or contain malware.