Having a really good password can't hack it against a smart hacker who knows how to deceive you into giving them sensitive information like passwords and credit card! Tricksters typically send phishing emails containing phishing links to gain access to your usernames and passwords.
One of the most popular email phishing scams is "fake Paypal emails" that look and sound like genuine Paypal communications but when you hover over the email of the sender you can see it is not from Paypal. Scam artists get potential victims to click on their links by sending worrying emails along the lines of "your account has been suspended due to unauthorized login attempts. Login now" or "if you haven't authorized this transaction, click here to get a refund".
Other phishing scams include Google Docs phishing attacks, Fake Amazon email orders, Gmail phishing scams and many more. What's worrying about online phishing scams is how scammers are able to bypass email security spam filters too, which is why a solution like YubiKey makes perfect sense as it strengthens two-factor authentication using smart card authenticator technology.
In a nutshell, YubiKey is a universal 2nd factor (u2f) USB A security key that adds an extra layer of security to your online accounts. YubiKey has a small footprint and comes in a SIM card-like form factor (YubiKey 4 Nano) and USB stick form factor (YubiKey 4) that fits easily on a key chain.
YubiKey works by using a two-step authentication process where you save passwords into the key to use it as a verification  process to prove that you are the owner of the account. This makes it impossible for phishing scam artists to access your account because even if they get you password via  phishing scam they won't be able to access your account because only you have the key!
After entering your password as usual, you only need to insert the key into your computer/laptop USB port and tap the key to complete the two-step authentication process. YubiKeys essentially removes the need for retyping passwords as all you have to do is plug in your YubiKey, tap, and YubiKey does the rest for you.

What's neat about the YubiKeys is that the login process is kept simple with a seamless one-touch login. You can choose not to use two-factor authentication again after using it on a particular computer like a personal laptop by setting it to "remember me" so you won't get asked every time you log in.
YubiKeys works in Chrome, Firefox, and Opera web browsers, Facebook, Gmail, Dropbox and all U2F supported services like Digidentity, Dashlane, LastPass, Compose, PushCoin, and GitHub. To set up YubiKeys you need register and pair the key with each computer you plan to use. Then, select the online service (Facebook, Google, DropBox, etc) and follow their instructions on how to set up the key with their platform.
A worry one can have with a device like YukiKey is what happens if you lose the key? Luckily, you can backup yourself by using a second key as a backup (a bit like the second car keyfob), or you can use Google and Facebook generator apps (or text verification) which you can use to get a code which will let you log in. You can also print off backup codes, all of which can only be used once. You can print off the security codes from Google account security settings.