Mysterious & unwanted re-direction

Hi

A couple of months ago, when my WP site was in a subfolder, I noted some mysterious foreign folders in the root folder, like one called “silent”. I further noted Google brought some guests to some pages dealing with drugs content in this & the other subfolder. I deleted them. These folders were NOT in the WordPress folder sharing the location in root, but the site occupying root folder. I must say I have since then brought the WP site to root & deleted the other site.

That was a couple of months back. Today, I mistyped the password & and was led to the correct custom page not found page, as far as content is concerned, I noted the url was not however /page-not-found, but => /silent/buy-lamisil-tabs-online/about.html?instance=1
[This “?instance=1”, I guess is from the sucuri plugin]

If I remember well, I think if one inouts a false password, sucuri does not redirect to another page.

Because of the above incident, I always check the folders on the síte & this also forced me to check them again as well as posts, pages & categories & there is nothing like “silent” & the search does not find “lamisil”.

So my question is: where could this be coming from & how do I get rid of it? The .htaccess content is simple & WP original.

Furthmore & quite shocking, I just noticed some mysterious entries in Statcounter, which do not show site URLS but other foreign urls! When I clicked them, I find dirty content at these foreign URLS BUT using my site’s layout. The title is also highjacked at THOSE foreign URLS.
I note at these url also categories I do not even see when I go to my posts categories in the site admin panel

How do I urgently get rid of this?

The foreign URLS include http://bit.ly/1DLHnQY

Thank you in advance.