Two popular sites in the file-sharing space have disappeared without warning. BTDigg, a specialist service indexing BitTorrent's Distributed Hash Table, has entirely vanished with no site available whatsoever. BillionUploads, a popular file-hosting site, indicates some kind of intentional shutdown, but offers no hope that users can retrieve their files.

Four years ago a new kind of torrent indexing site hit the scene. While most other sites were carrying a database of torrent files uploaded by their users or culled from elsewhere online, BTDigg took a different approach by using DHT.

BitTorrent’s Distributed Hash Table, to give it its full title, is a system supported by most major BitTorrent clients. It allows users to find peers sharing the same files without needing a centralized BitTorrent tracker. In December the system was relied upon heavily when most of the main public trackers went down unexpectedly before returning last month.

BTDigg offered a special search engine that allowed users to trawl DHT in order to find content and download via magnet links. It was even possible for users to find content that hadn’t been uploaded to public trackers yet but was just being shared in DHT-enabled torrent clients.

“We think that the Internet’s moving towards decentralized and distributed systems and we would like to contribute to it by creating BTDigg,” the site’s creator told TF in a 2011 interview.

But now, just a couple of weeks’ shy of the site’s fourth birthday, BTDigg is no more. The site has disappeared with users now confronted by a page that simply won’t resolve. All mail to BTDigg bounces and the site’s Twitter account has been dead for some time.

The shutdown comes as a surprise. Unlike RapidShare, for example, which will close shortly due to diminishing visitor numbers, in January BitDigg pulled in more traffic than it had done in the past 12 months, despite being subjected to web blocks in the UK. A site voluntarily pulling the plug during good times is a pretty rare occurrence.

But while BTDigg had been riding high and doing relatively well, the same cannot be said about file-hosting site BillionUploads.

After enjoying success its popularity began to wane, and in the past 10 months the file-hoster dropped from an Alexa global ranking of 2,000 to around 8,000 recently.

BillionUploads had previously proven itself a hit with many Internet users, often through their use of other services. As can be seen from the data below, much of the site’s traffic came from movie indexing and streaming sites such as Icefilms, Primewire and Movie4k. These sites offered movies with BillionUploads as one of the key sources.

Recently, however, users linking into BillionUploads via Icefilms, to name just one location, found that content wasn’t forthcoming and a visit to the site itself now reveals an ominous notice. It’s very low on detail, provides no explanation, and certainly doesn’t inspire confidence in any kind of return.

This sudden demise will be problematic for any users who stored content on the site and now expect it back, but to be fair this can’t really be compared to the unannounced shutdown of a Dropbox-type operation.

It’s fairly likely that many users of the file-hoster will have expected this kind of outcome and are already viewing movies on another site. For those looking to retrieve content, however, holding collective breaths for too long might be ill-advised.

Update: BTDigg is back online after nearly a week of downtime.