We are currently facing a Japanese keyword hack issue on our website (https://example.com/). The issue is faced on 25-11-2019 when we got the mail that shows someone is the new google search console property owner. After, Our almost all URLs converted into the Japanese language. We had resolve website recovery from the developer, submit a new sitemap and manually fetched pages from the Google search console.
Our traffic went down for 2 days and after recovery, traffic comes back. Even when we type the name of our company then it does not show on the listing but after recover, it has displayed and the traffic is back.
The problem is that there is 70-80 URLs are present on the google search index now which is not available on our website database. Some of that is below. https://example.com/?/90ZWNobm9zdGFja3MuY29tL2luZGV4LnBocD87665db29/nost=102819332.meg https://example.com/?/90ZWNobm9zdGFja3MuY29tL2luZGV4LnBocD83cba313f/nost=10715921.meg https://example.com/?/90ZWNobm9zdGFja3MuY29tL2luZGV4LnBocD81eacb5e1/nost=100830546.meg https://example.com/?/90ZWNobm9zdGFja3MuY29tL2luZGV4LnBocD8a6297ffc/nost=107023915.meg https://example.com/?/90ZWNobm9zdGFja3MuY29tL2luZGV4LnBocD86c6db77c/nost=10613755.meg
We had removed that URLs from the search console and resubmit the sitemap. Also used URL parameter tools and exclude parameter "?/", "nost" on 29-11-2019, 5-12-2019 but the issue remains there.
The main issue is website traffic is back but the spam URLs are still shown on the google index and also new spam pages are generated and indexed on google. Most of the traffic from that spam URLs are from japan.
What we can do? Please give the solution so that we can remove that URLs from the search index and maintain the visibility of our site. We think that this issue is also faced by other sites and this solution may helpful for them.