New WhatsApp notification alerts you when the web client is open
Clicking on the notification will close the WhatsApp Web client on your computer, eliminating the risk. The notification cannot be disabled, and on Android it shows up on the notification bar with the same icon used to denote a message. That is sure to confuse Android users who could understandably think that they have unread messages to view on the app.
For those who missed the news, WhatsApp Web is an extension that allows you to sync your WhatsApp account on your computer. It is available for those with a phone running Android, iOS 8.1 or higher, Windows Phone 8.0 and 8.1, Nokia S60, Nokia S40 EVO, BlackBerry and BlackBerry 10. You will need to have the latest version of Chrome, Firefox, Opera, Safari or Edge on your computer. You also must be running the latest version of WhatsApp beta, 2.16.86. If interested in this beta version, click on the sourcelink.
source: WhatsApp via AndroidPolice