Question: Today I opened a social network and saw that one of my coworkers, let's call him Bob, posted a piece of source code of one of our projects.

The quick video is blurry, so it's hard to actually read it, but not impossible.
IANAL but I'm pretty sure that this is illegal.

There is no way that anyone else in my company will see it since no one has that social network but for me.

As I see it I have 3 options:

* Act as if I did not see it
* Talk to him in private and make him realize how potentially bad this could end up being, for him and the company.
* Report this to my boss.

**Additional information:**

This is the first work experience for Bob and he has been working with us for less than 3 months.

My question is: **How should I behave in this situation?**

I really don't want to escalate this, but if something bad happens because of that post, and my boss finds out I knew about it, I think I would be in legal danger.

Answer: 
How did he post the code? Screen shot? Video with his monitor in the background? Are machine readable text that I could copy, paste and compile? You say "it's blurry and hard but not impossible to read", so I assume it is a video with a monitor visible? 

If that is the case, then let's be serious here: Nobody will be interested in that piece of code. The source code that I'm working on is highly valuable, but if one page of it is shown in a video, it's not of any use to anybody. One page, randomly picked, without any context, is completely useless to anybody. Nobody will even try to copy it. 

Unless there are comments in the code that you wouldn't want to share like "this function contains the code where we siphon off the user's address book and send it to our server, and the losers will never find out", then very little harm is done.
Other options:

* Mention the topic of "social networks"in a casual way at lunch and clearly state that you don't think that anything related to work should be visible in a video posted there.