Has my site been hacked ?

Please scan your site at Sucuri and if infected with malware read this:

https://codex.www.ads-software.com/FAQ_My_site_was_hacked

Already did that, but redone it after your reply. Sucuri till indicates that the site is clean and not blacklisted.

If you post a link to your site, it will make it easier for people here to help figure out what the problem may be.

EDIT — SORRY – just saw it!

Looks like some HTML mark-up errors :

https://validator.w3.org/check?uri=http%3A%2F%2Fwww.gds.umontreal.ca%2Fblog%2F2012%2F10%2F25%2Flethique-antipathique-de-la-recherche-universitaire%2F&charset=%28detect+automatically%29&doctype=Inline&group=0

https://codex.www.ads-software.com/Validating_a_Website

Wow, thanks ! I can clean up some of the errors indicated (for instance those that appear in the footer, or the widgets), but many are not accessible to me. I mean, I understand that some tags are erroneous, but they are not visible through the dashboard. How do I find where the errors come from ? And what did cause the code to change in the first place (everything was working fine before last week !) ?

I have been comparing a few files in my actual WP, like comments.php, archives.php, style.css, with some of a backed up version, but so far I have found no difference between both. Any idea where I should look for ?

Thanks !

You could try reinstalling your theme — it does look like whichever template is being used on that page is not quite right – the sidebars are in the footer?

Yeah ! I resolved it myself !

The problem was not the theme, it was a plugin that, for an unknown reason, started to generate some dirty code. So out with ByBrickColumns ! I promise I will slow down my plugins consumption…

Thanks all !