Troubleshoot adware after update os el capitan on Mac book air

[Vince64]

Hello,
After an OS update to el capitan on my macbookair yesterday, I got a popup on my screen and also in my browsers when trying to go online... Both of them slowing down my computer and blocking any web navigation.
(I send this from my Imac).
I have downloaded Malwarebytes and could let it run, but no result, I installed also Avira and also no virus or malware founded after complete scan.

All transfers to my iMac are going via USB sticks at this time.

Thanks for helping

 

[Atlas147]

Can you take a screen shot of the popups? Maybe we can get a better look at what it is

 

[Vince64]

 

[Atlas147]

I check the URL it looks like a legitimate website, maybe you are connecting to something other than your home router and it requires you to login? Check your network to see if you are actually on your router or another device, it could be the cause

 

[Vince64]

Hope it could be the reason. I checked the router, it's the good one right now and no popup or problem more than 1 hour ago.
Maybe it took a lot of time before the connection was back automaticaly, I didn't give a look on this ! No warning message also.
And so long it was'nt right, I got this from my provider. Never happens before !

Thanks for your time about this no adware or virus problem...

 

[Ink]

As a precaution, you can scan with Malwarebytes Anti-Malware (Free Anti-Malware Detection & Removal Software for Apple Macintosh Computers) - it's free.

You can also share your computer's security and get feedback to improve your setup:

• Security Configuration Wizard

 

[Chromatinfish 123]

HI, Could you please give us some more information? Likes
- How frequently do these popups come up?

- When do they come up?

- Do they come up just when you start, or every time you try to visit a webpage it comes up? Or it locks you from going anywhere altogether?

 

[jamescv7]

How to reset Safari settings and othes

Try to clean and refresh, however the site seems asking to enter WiFi credentials which depends on your internet connection as reason why it blocks sites to access. (normal from ISP)