Que signifie cette erreur nginx "cycle de réécriture ou de redirection interne" ?

tail -f /var/log/nginx/error.log
2013/05/04 23:43:35 [error] 733#0: *3662 rewrite or internal redirection cycle while internally redirecting to "/index.html", client: 127.0.0.1, server: _, request: "GET /robots.txt HTTP/1.1", host: "kowol.mysite.net"
HTTP/1.1", host: "www.joesfitness.net"
2013/05/05 00:49:14 [error] 733#0: *3783 rewrite or internal redirection cycle while internally redirecting to "/index.html", client: 127.0.0.1, server: _, request: "GET / http://www.qq.com/ HTTP/1.1", host: "www.qq.com"
2013/05/05 03:12:33 [error] 733#0: *4232 rewrite or internal redirection cycle while internally redirecting to "/index.html", client: 127.0.0.1, server: _, request: "GET / HTTP/1.1", host: "joesfitness.net"

Je reçois ces messages dans le journal des erreurs de nginx, je n'ai pas de sous-domaine "kowol", je n'ai pas de liens vers qq.com ou joesfitness.net sur mon site. Que se passe-t-il ?

Editer : Nginx default config :

server {
    listen   8080; ## listen for ipv4; this line is default and implied
    listen   [::]:8080 default ipv6only=on; ## listen for ipv6

    root /usr/share/nginx/www;
    index index.php index.html index.htm;

    # Make site accessible from http://localhost/
    server_name _;

    location / {
        # First attempt to serve request as file, then
        # as directory, then fall back to index.html
        try_files $uri $uri/ /index.html;
        # Uncomment to enable naxsi on this location
        # include /etc/nginx/naxsi.rules
    }

    location /doc/ {
        alias /usr/share/doc/;
        autoindex on;
        allow 127.0.0.1;
        deny all;
    }

    # Only for nginx-naxsi : process denied requests
    #location /RequestDenied {
        # For example, return an error code
        #return 418;
    #}

    #error_page 404 /404.html;

    # redirect server error pages to the static page /50x.html
    #
    #error_page 500 502 503 504 /50x.html;
    #location = /50x.html {
    #   root /usr/share/nginx/www;
    #}

    # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
    #
    location ~ \.php$ {
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        # NOTE: You should have "cgi.fix_pathinfo = 0;" in php.ini

        # With php5-cgi alone:
        fastcgi_pass 127.0.0.1:9000;
        #With php5-fpm:
        #fastcgi_pass unix:/var/run/php5-fpm.sock;
        fastcgi_index index.php;
        include fastcgi_params;
    }

    # deny access to .htaccess files, if Apache's document root
    # concurs with nginx's one
    #
    #location ~ /\.ht {
    #   deny all;
    #}
}