add/delete plugin function redirects to bad web site

You may have been hacked:
https://codex.www.ads-software.com/FAQ_My_site_was_hacked
https://www.ads-software.com/support/topic/268083#post-1065779
https://smackdown.blogsblogsblogs.com/2008/06/24/how-to-completely-clean-your-hacked-wordpress-installation/
https://ottopress.com/2009/hacked-wordpress-backdoors/

I have the same thing happening to me. I am still trying to find out what and where it is. I have scanned all my files and database content with AVG and MalwareBytes, but it does not show up as a virus. The issue I have is it tries to go to the checkprivacy.ru when I go to https://www.mysitename.com, but is ok when I leave off the www. It also does some strange things when I go to the plugins section, so I assume it is in there, too.

both must check .htaccess file, delete it and create it again, then you MUST secure your wordpress installation, and ask for bad files to your hosting provider.

It looks like a php “trojan” script in your hostings ??

any advice as to how to find the trojan? would it be in my site’s files or the hosting sites files?

Yes, please any advice… I have read all the links ESMI provided and there does not appear to be anything that I can find in my installation. I have asked the hosting company to check the .htaccess file and they appear to have fixed a redirect issue there, since now entering https://www.sitename.com goes to sitename.com instead of the hacker domain.
When I try to use the Add New Plugin feature, though, I still get an attempt to run something on a .ru domain and the page does not display properly.

my hosting provider has also elimiated the offending htaccess file and so far i have not had any problems. Crossing fingers….thanks to all for the advice…