Hi @Bawarmf,
The most likely explanation is that your site was not configured correctly with the proper security precautions, as per our recommendations here: https://docs.pkp.sfu.ca/admin-guide/en/securing-your-system
there is this also a thread where a user reported this too: OJS is being improperly redirected to a betting site - #9 by edwardsafari
That provides some specific recommendations on how to mitigate the issue.
-Roger
PKP Team