Usually these threads are placed in the Wrong Planet forum for discussing issues with the website. Your computer is not infected by that pop-up, it's a phishing attempt to get to to divulge your password etc, so that hackers can steal your data. Never supply personal information or do as they request. Restart your computer then run your anti-virus and then Windows Defender, have a look at the Defender report to see if they have quarantined anything.
The popup scam you have mentioned has been happening for quite some time - the front page is infected.
Question: did you access the front page from within Wrong Planet or by googling Wrong Planet? Has it happened with one mode only of access or both?
Look at the threads active on the other subforum for more comments on that particular infection.