Attackers could use the information taken from Yahoo to obtain access to other online accounts that contain even more sensitive information.
Avoid using common passwords like 1-2-3-4-5-6 or p-a-s-s-w-o-r-d (see more here), and include a mixture of numbers, letters and characters.
Adding a second type of authentication, like a one-time code sent over text message or generated by an app, can greatly secure your online accounts.
Yahoo is recommending people turn on its two-factor authentication tool: Yahoo Account Key.
The company has already disabled any unencrypted security answers on its accounts.
If you frequently use the same security questions and answers for other online accounts, you'll want to change those, as well.