Elementary S02E03 - S02E05

Elementary S02E03 - Ancient History

Note: Netflix inverses episode 2 and 3 of the second season. If you are looking for "Solve for X", read the review of Elementary S02E02.
This episode didn't have any interesting computer science questions.

Elementary S02E04 - Poison Pen

Netflix inverses episode 4 and 5 of the second season. If you just finished watching the 4th episode on Netflix scroll down.
This episode didn't have any interesting computer-related aspects.

Elementary S02E05 - We are Everyone

Note: Netflix inverses episode 4 and 5 of the second season. If you are looking for "Poison Pen", see above.

The plot of this episode revolves around a fugitive who leaked sensitive information to the media. It is likely inspired by the Snowden leaks. Snowden, an FBI contractor, leaked data that revealed a global surveillance programs. However, contrary to the character in this episode, Snowden never threatened to release information that could jeopardize the safety of US agents (or other humans). Snowden's case is interesting, as the revealed programs were often found to be illegal. As such, many people praise Snowden's courage to speak up (requiring him to seek asylum in Russia), whereas others blame him for releasing sensitive information (potentially not exhausting all possible legal avenues).
Another famous recent leak that probably influenced this story, was the one perpetuated by Chelsea Manning. Manning leaked classified military documents to Wikileaks (with editor-in-chief Julian Assange).

The authors use the leaking-angle to bring in a hacker-group called "Everyone". These, self-described cyber-activists, want to protect Ezra, the leaker. I'm guessing that "Everyone" is inspired by Anonymous, a real-world network of activists and hacktivists. In any case, there are certainly online groups that see it as a moral duty to distribute this kind of information.

"Everyone", and in particular its member Defenestrator, are protecting Ezra. Since users are anonymous on the online forum, Holmes uses online chats to extract enough information to identify Defenestrator. At some point he extracts the approximate location of the target (3 block radius), and then got another person to reveal who, in that area, purchased "high-end equipment, suitable enough for hacking".
The last part shows a misunderstanding of how hacking works: one doesn't need sophisticated hardware to launch very efficient attacks. Hackers might have good equipment because they consider computers their tools, but the hardware wouldn't be special. Gaming computers are usually much more powerful.
When hackers manage to take down important sites or services, they don't really use their own equipment. Instead they control thousands of exploited computers to do the attack on their behalf.

4 of the 20+ ordered Pizzas.

Later in the story, "Everyone" starts to mess with Holmes and Watson's life. They order more than 20 pizzas in their name, and hack their computers and online accounts. While slightly exaggerated, this scene actually felt realistic to me. Some cheap tricks could be done by anyone: ordering pizzas for someone else is trivial (although it is a stretch that the pizza-company wouldn't check for 20+ pizzas first). Similarly, one can easily publish offers (even sex-encounters) on specific web-sites, leading to incessant phone calls.
Other tricks are harder to pull off: changing data on the dating-website, or on other social networks, is much harder. Unless "Everyone" hacked directly into these sites (unlikely), they would need to get the password from somewhere. The easiest way is to use a phishing mail: simply ask the victim for the password, but disguise who you are. Unfortunately, many people use the same password for different web-sites, and therefore getting the password once is enough to screw with the victim.
There are, however, two things that don't fit:
1. Holmes, being a computer expert, wouldn't have the same password on different sites, and
2. he wouldn't be trapped by a phishing mail.
Another angle of attack consists of compromising Holmes' and Watson's machines. On up-to-date machines this is hard, but a big hacker-group like "Everyone" could definitely get this done.
Once the machines are infected, hackers have access to every key-stroke and can thus listen for passwords, ...
A single individual would have a hard time doing as much damage as was shown in the show, but a skilled collective could do so.