Foreign decks repeatedly appearing in my AnkiWeb collection after sync

Anki Syncing & AnkiWeb
1

Hi,

I’m reporting a recurring synchronization issue that may also have security/privacy implications.

This is now the third time that content I did not create or import has appeared in my Anki collection after syncing with AnkiWeb.

The foreign content is not corrupted or random. These are complete, coherent decks that appear to belong to another user. Interestingly, the decks are in Portuguese and contain medical-study material, which is also the field I study.

On one previous occasion, the problem was much more severe: my entire collection was replaced by another person’s complete and coherent collection.

Today it happened again. A new deck called “Pediatria” appeared during synchronization.

The sequence today was:

  1. My desktop Anki collection was normal and did not contain the “Pediatria” deck.
  2. My iPhone collection was also clean before syncing.
  3. I started a synchronization on the iPhone.
  4. During/after that sync, the foreign “Pediatria” deck appeared on the iPhone.
  5. My desktop computer had not yet been synchronized, so I was able to preserve a pre-incident backup of my normal collection.

I am absolutely certain that I have not shared my AnkiWeb account, and I have not knowingly left my account logged in on another person’s device.

I have preserved:

  • a full .colpkg backup of my collection from before the incident;
  • the foreign Pediatria.apkg deck;
  • my desktop collection in its clean pre-sync state;
  • the approximate time at which the incident occurred.

The foreign deck itself is coherent medical content in Portuguese rather than random database corruption.

Because this has happened three separate times, including one incident where my entire collection was replaced by another user’s collection, I am concerned that either:

  • an unknown client/session is somehow syncing to my AnkiWeb account, or
  • there may be some problem involving account/session or collection isolation on AnkiWeb.

I do not want to assume which explanation is correct. I would appreciate it if someone from the Anki team could investigate the server-side history/logs for my account and determine which client/session uploaded the foreign deck to my AnkiWeb collection.

In particular, is it possible to determine:

  • when the “Pediatria” deck was introduced into my AnkiWeb collection;
  • which client/device/session uploaded it;
  • whether there have been syncs from devices or sessions other than mine;
  • whether the previous replacement of my entire collection could be related to the same issue?

I can provide the pre-incident .colpkg and the foreign .apkg privately if they would be useful for investigation. I would prefer not to upload the foreign deck publicly because it may contain another user’s data.

Thank you.

2

I’ve never heard of anything like this happening through the AnkiWeb servers – so the first thing I’d encourage you to do is change the password for your AnkiWeb account. That will ensure that only you and your authorized devices, will have access to sync with your account. Do that on your account settings page – https://ankiweb.net/account/settings – and then update the credentials on each of your devices the next time you sync.

This obviously shouldn’t be happening, even one time – but yes, you should can always be able to restore your collection from the automatic backups on one of your devices.

Thank you for everything you’ve gathered so far. I want to investigate that further before I get any of it from you.

Questions and general maintenance –

  1. Do you know approximately when these other incidents were? I’m just looking for a general sense – like 3 times this month, 3 times this year, etc.

  2. Can you narrow the time-frame for when this most recently happened? I’m looking for a specific date-time when you know your collection was correct and in-sync with AnkiWeb, and a specific date-time when you found this other material in your collection after syncing. [Please include the time zone or convert it to UTC/GMT.]

  3. You first spotted this in AnkiMobile this time – has that been the case for all 3 times, or has it also been first seen in desktop Anki?

  4. When you leave desktop Anki, do you close it? Or is it left open and connected to the internet? If you leave it open, do you have any add-ons that sync automatically?

  5. Do you have any decks in your collection that update through 3rd-party services like AnkiHub, AnkiCollab, CrowdAnki, etc.?

  6. Since the same deck has appeared multiple times, you should run Tools > Check Database to make sure nothing is floating around hidden in there. I’ll be interested to know whether any message returns from the database check.

  7. Even though you’ve restored your collection database, run Tools > Check Media > Delete Unused Media to clean up any media not connected to your own decks. I’ll also be interested to know whether you’re able to identify specific media that doesn’t belong to you decks.

  1. I can see how alarming that would be. Do you recall, on that occasion, whether you were given a one-way sync notification (and needed to choose between upload/download)? Obviously you would have had no idea that a different collection would download – but would be useful for us to know whether you got the expected messages.
4

Hi Danika,

Thank you for your response and for looking into this.

I have already changed my AnkiWeb password and updated the credentials on my devices.

I want to provide an important update that I discovered after my original report, because it seems highly relevant to the investigation.

I was able to identify the owner of the “Pediatria” deck that appeared in my collection. It belongs to a friend of mine who has her own independent Anki collection.

Initially, this seemed impossible because:

  • she has never logged into my AnkiWeb account;
  • I have never logged into hers;
  • we do not share Anki profiles or devices;
  • her current Anki installation is not connected to AnkiWeb.

However, we discovered something unusual: in her local Anki backup folder, there was an automatic backup containing what appears to be my entire Anki collection.

We preserved this backup and have not modified it.

After comparing the collections, it appears that this was not just similar content. The backup from her computer shares the same collection structure and the same underlying Anki objects (notes/cards) as my collection. Additionally, the “Pediatria” deck that later appeared in my collection corresponds to the same deck she created.

This makes me think this may not simply be a case of an unknown device accessing my AnkiWeb account. It may involve some unexpected crossover between two independent collections.

The timeline for the most recent incident:

  • My desktop collection was correct and synchronized on September 16, 2026 at approximately 08:41 UTC-3.
  • My iPhone collection was clean before synchronization.
  • During synchronization with AnkiMobile later that day, the “Pediatria” deck appeared.
  • The deck was not created or imported by me.

I also want to add information about a previous incident, because it may indicate this is not limited to my friend’s collection.

On a previous occasion, my entire Anki collection was replaced by a completely different collection. This was not my friend’s collection; it appeared to belong to another person.

That collection:

  • was complete and coherent;
  • was in Portuguese;
  • contained medical-study material.

In that previous incident, I remember receiving the one-way sync warning and choosing to upload my local collection because my desktop version was the correct one.

At the time, I assumed it was an isolated synchronization problem. However, after discovering that my friend’s collection appears to have crossed into mine now, I wonder whether these incidents could be related.

To answer your questions:

  1. The incidents occurred:
  • insert approximate dates if known
  1. Most recent incident:
  • Last confirmed correct/synchronized collection: September 16, 2026, approximately 08:41 UTC-3.
  • Foreign deck detected: September 16, 2026, approximately [insert time] UTC-3.
  1. This most recent incident was first noticed in AnkiMobile. Previous incidents:
  • insert whether noticed on Desktop or AnkiMobile
  1. I normally close Anki Desktop after studying. It is not left open and connected to the internet. I do not use any automatic sync add-ons.
  2. I do not use AnkiHub, AnkiCollab, CrowdAnki, or any other third-party synchronization service.
  3. I will run:
  • Tools → Check Database
  • Tools → Check Media → Delete Unused Media

and report the results.

Regarding the previous incident where my entire collection was replaced: yes, I received the one-way sync prompt and selected upload because my local collection was the correct one.

I have preserved the following files:

  • my clean collection before the recent incident;
  • my collection after the foreign deck appeared;
  • the foreign “Pediatria” deck;
  • my friend’s backup containing the unexpected copy of my collection.

I can provide these files privately if they would help with the investigation.

I understand that this is an unusual situation, and I do not want to assume the cause. However, the fact that the foreign data appears to be real, coherent Anki data belonging to other users rather than random corruption seems relevant.

Thank you for your help investigating this.

Best regards,
Italo