If ads or virus warnings keep popping up in the corner of your screen, a site has permission to send you notifications. Remove that permission in Chrome’s settings. It takes about a minute.
Faster: copy chrome://settings/content/notifications into the address bar and press Enter. Then go to step 4.
Step 1
Open Chrome’s menu ⋮ in the top right corner (1) and click Settings (2).

Step 2
On the left, click Privacy and security, then Site settings.

Step 3
Under Permissions, click Notifications.

Step 4
Scroll down to “Allowed to send notifications” and find the site. Click ⋮ next to it (1) and choose Block (2): the site can’t ask again.

Done. The notifications stop at once. To stop all sites from asking, choose “Don’t allow sites to send notifications” under Default behavior.
The pictures are simplified and show Chrome for Windows. The menu names are Chrome’s own.