According to Guardian (Thu 17 Jan 2019), this is a typical “webcam blackmail” or “sextortion scam”. From the depths of internet (darknet) those criminals have mined some old, not so good passwords, used maybe even years ago.

Nothing happened, nothing was hacked, and no spy-/malware found on my devices. Not that I was worried because any of those accusations made on the message. The real concern was the security of all work related stuff and private correspondence between me and other people. In this case the password is probably the same that was compromised somewhat ten years ago, when my Twitter account got hacked.

And if you ever get such email, I recommend ignoring it. The worst thing one could do is to reply. What you can and should do instead:

1) If you indeed still use such endangered old password anywhere, then change it immediately!

2) You can also check if some of your old passwords are listed at Have I Been Pwned database. But even if you get "green light", change that password anyway.

3) To assure yourself that your computer is not hacked, update your operating system. Install some Internet Security software, if you do not have one yet. Update that software if you have. Run full inspection on your computer. Some of the software providers give free "online check", like F-Secure.

4) Although the accusation to become spied via webcam is ridiculous, such spyware still exists. The solution is simple. Put a sticker over your web cam when you are not using it. Microphone is another risk on laptops and mobile devices. There are for example claims that companies like Google secretly spies users via microphone, to provide more targeted services (advertisements). I find that very unlikely, and only as rumor spread by competitors and those who sees conspiracy theories everywhere. But again, technically anything is possible. By keeping your operating system and software up-to-date, you should be on safe side. At least do not say aloud: "My ipernity account password is x.", onto your device microphone ;-)

5) Do not visit any web sites that could endanger your device and privacy! Do not open any links on email, that you are not sure about! Use only trusted sources.

6) Consider reporting blackmail as a crime. There is maybe an online service provided by local/national police to do that. You may wish to mark it as less urgent issue. Such criminals at least can hide their tracks, usually, So, most likely they never get caught. But blackmail is a blackmail, no matter what. At least it is "intimidation" (cowing, illegal threat).