Hello!
If this "virus alert" is popping up while you are using Chrome on your mobile device these are spam attempts. Do not click or attempt to do anything it says. These tricks will lead to more harm than good. The odb.org site might be fine to browse, but perhaps you accidentally clicked one of the side ads while reading. These will usually spawn the exact type of behavior you described above. When you are on the site causing the issue look in the top right corner of your webpage. There should be a box to the left of a set of 3 dots stacked on each other. Click the small box and it will zoom out slightly giving you ability to "X" out on the site you are on. Never download anything it asks you to.
If the behavior continues to happen, you may need to look into an alternative browser on the Google Play Store that has adblocking built in.