Twitter : bug or hacked ?

On Sunday, 22 September 2013 a lot of users are complaining of websites asking to download a mysterious file named "widgets_tweet_button.html.torrent" or sometimes "widgets-tweet_button.html.torrent" when browsing from Google Chrome or Firefox on Windows. The well-known TechCrunch website seems to suffer from this bug, on pages like this one (after multiple refreshes). So does BusinessInsider (here).

All websites that seem "infected" offer the same Twitter sharing link. The french website CommentCaMarche.net managed to stop this by simply temporarily removing the share button, which seems to be a workaround to this problem.

A lot of tweets refer to this problem without knowing what's happening or what to do:

Many Wordpress users state that Official Twitter Button has problems. Twitter seems indeed to randomly give a torrent file as a result instead of the classic share button!

Here is the transcript of what Twitter should return:

curl -I -k http://platform.twitter.com/widgets/tweet_button.html
HTTP/1.1 200 OK
Cache-Control: no-cache
Last-Modified: Thu, 19 Sep 2013 23:54:42 GMT
ETag: "86e25ce34214e039e32bd33c7aaeefa6"
Content-Type: text/html; charset=utf-8
Date: Sun, 22 Sep 2013 20:19:01 GMT
Connection: keep-alive
P3P: CP="CAO DSP LAW CURa ADMa DEVa TAIa PSAa PSDa IVAa IVDa OUR BUS IND UNI COM NAV INT"

Here is what Twitter sometimes gives as a result:

curl -I -k http://platform.twitter.com/widgets/tweet_button.html
HTTP/1.1 200 OK
Accept-Ranges: bytes
Content-Disposition: attachment; filename=widgets/tweet_button.html.torrent;
Content-Type: application/x-bittorrent
Date: Sun, 22 Sep 2013 20:19:03 GMT
Last-Modified: Sun, 22 Sep 2013 15:21:48 GMT
P3P: CP="CAO DSP LAW CURa ADMa DEVa TAIa PSAa PSDa IVAa IVDa OUR BUS IND UNI COM NAV INT"
Server: ECS (ory/439A)
X-Cache: HIT
Content-Length: 301

Is this a bug of Twitter? Was Twitter corrupted? At this time a lot of questions are being asked on Twitter and bulletin boards, but still no real answer...

September 23rd update: The torrent file seems to contain twitter button's HTML code only.