problem in login -> redirects to malicious page

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Hello!

Lately, I have a problem with my concrete5 pages. When I go to the login, after add my user and password and click the Log in button, the page redirects to another page, generally a porno site.

I've searching in the database, in files and can't find the source of the redirection.
I'm using miser (latest version) and latest version of concrete5...

The htaccess file is fine, so I'm clueless where is the problem. Can you help me?

Thanks in advance.

prpdesigns