Using SD Maid, I was looking around with file explorer and came across this directory in the efs folder, and I have no clue what it is, if its malicious or not. Its the only directory in the efs folder with a name that isnt clearly defined. (like modem, data etc) I tried Googling the directory and file names but got nothing.

Device info: USC Samsung Galaxy S5 (SM-G900R4, Qualcomm, codename klte); rooted and slightly customized using hidden menu settings; software up to date.

This is how it appears in SD Maid:

/efs/U0BwJ04kmkmm-Bg7zUZgoEY7pn8_/zm0WY41Y7rpx3kcVTTDWeh8VFRU_ (size: 1.05kb, date 1/1/14)

/efs/U0BwJ04kmkmm-Bg7zUZgoEY7pn8_/qen2gEqW2A+OTD0KpoESJiYnrk_ (size:1.05kb, date 1/1/14)

I don't know, if anyone that has seen it before.

  • I too have those files, though I don't know their usage. – Death Mask Salesman Aug 28 '16 at 22:12
  • It's quite hard to read your question, can you reformat it please? – Bálint Babics Aug 28 '16 at 22:25

Samsung devices' EFS partition

It is a place that the device stores important data like WiFi and Bluetooth MAC addresses and your IMEI number (nv_data.bin).

What is EFS?

  • The EFS refers to a folder called EFS which can store information like meid, imei, serial number, config, diag settings and radio settings, etc in an encrypted format at the file system level stores. So it is very neccessary for us to backup EFS before flashing ROMs.

How will you lose the EFS folder?

  • As far as I known, you always lose your EFS by mistaken operations. For example, flash ROMs or wipe data using an uncorrect method. Even wrong power on & off ways like taking out the battery to force shutdown as starting could corrupt your EFS, too. Rooting and flashing ROMs usually have no influence on EFS data, but you know everything can happen in the real word. There are some ways you can check whether your EFS folder is lost: inputting *#06# on dialler, going to settings/about phone/status or checking mac address.

What results if you lose the EFS folder?

  • The loss of the EFS folder may bring about an incredible disaster on your device such as no imei information, base band unknown, no radios and so on which mean your device will no longer be recognized by your carrier.

How to back up the EFS folder?

  • There are too many tools you can use to back up the EFS folder. All of them work in a similar way, so we will just introduce one tool called Custom Recovery here. Everything has risks. we are not responsible for the following method. Please act with caution!
  • Bofore backing up the EFS folder you need make sure your Andriod device is rooted. Then, install Custom Recovery on your device. Open the Custom Recovery, select the Backup option, and go on select the paritions containing EFS, then "Swipe to Back Up" to begin the backup process.


  • It seems that OP knows about what's EFS. What they ask, is whether the files inside the /efs/U0BwJ04kmkmm-Bg7zUZgoEY7pn8_ / are safe. – Death Mask Salesman Aug 28 '16 at 23:34
  • 1
    @DeathMaskSalesman Doesn't look like so (I made a pending edit to OP but doesn't change the meaning). Also one's not supposed to touch anything in EFS. – Andy Yan Aug 29 '16 at 8:10

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