引用自 Aaron CSGOReactor.com：

引用自 Glimmer：

There have been a number of people who went on a VAC enabled server and have not been banned last I checked so probably not.

Are there confirmed sources of this?

Check the account of the people who say they connected to VAC enabled servers while running IM.
https://psteamcommunity.yuanyoumao.com/groups/idlemastery/discussions/0/517142253860851519/
https://psteamcommunity.yuanyoumao.com/groups/idlemastery/discussions/0/620700960790713056/
https://psteamcommunity.yuanyoumao.com/groups/idlemastery/discussions/0/604941528478458413/

It's still strongly advised not to run IM if you want to play a VAC secured game, but that's as much of screwing up your drop rates as it is the possibility Valve will suddenly change their minds.

There have been a number of people who went on a VAC enabled server and have not been banned last I checked so probably not.

Double check your Badges page to make sure you have drops remaining. If you're not sure where to look, the yellow boxes in this image show the correct location.
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=503188239

Free-2-Play games do not give any free cards just for adding them to your Library, you must spend 9$US for each drop. Non-F2P games give half (rounded up) the number of cards in the set. Duplicates will count against your allotment of free cards. Trading/Selling/Using cards will not grant you additional/replacement cards.

Idle Master only runs games that have drops remaining. F2P games do not give any cards just for adding them to your Library. If you want drops for a F2P game, you must spend 9$US for each drop.

引用自 Syrah「✔」 彡：

(Still SUPER weird tho that only people who used Idle Mastery were affected...)

According to This Post there were people who never used an idling program who were affected. I don't know any of them personally so I can't vouch for their veracity.

引用自 R3cX：

And no one can see my information ?

Correct, your information is safe.

Yes. From the FAQ:

Can Idle Master be used to pad my playtime of a particular game?

The steam-idle.exe application that's included with Idle Master can be given a command line argument of the appid of the game you'd like to idle. For example, if you'd like to idle Team Fortress 2 for playtime, you can simply run "steam-idle.exe 440" from a command prompt. There is no user interface for this, it must be done through the command line.

On it's own, Idle Master can't get you a VAC ban since it never connects to a game server. If you leave it running and you decide to play a multi-player game on a VAC enabled server it's possible to get banned although I've never heard of it happening.

Using the python script on Linux. Got cards for Blood of Old at .2 and 1.2 hours. 1 card left. So far, my Badges page has correctly reported the number of cards remaining for Blood of Old and Labyronia 2 each time I checked.

Update:
Last card from Blood of Old dropped at 2.2 hours.

There have been many reports that idling multiple games simultaneously will prevent cards from dropping.

Previously, you needed 2 hours of playtime before normal drop rates started (to prevent Refund policy abuse). Since that initial 2 hours had a 0% chance of giving cards, it didn't matter if you ran 1 game of 30 games. Starting a couple days ago, some games/accounts/whatever do not have that initial 2 hour requirement.