I found a few "unofficial" Lollipop ROMS floating around the internet.

I don't know how reliable are they, or how many viruses are there.

All I want to do is to play with it a little. I'm thinking of making an NANDROID backup, flashing the rom, playing with it a little (with no private information placed there), and restoring the NANDROID.

Is this safe? Can a malicious Rom writer intercept any attempt to flash a Recovery and keep itself on the phone (sort of like a rootkit)?

  • I have never heard of malicious roms. Also, for a hacker it would be easier to just write a rootkit for the system. Anyways, just test a rom which has already been tested by a big number of people – maxpesa Jan 9 '15 at 12:57

No, it can't.

As long as you don't flash any new firmware files (like we have to do with the HTC One M8 to get it on lollipop) you should be fine with a nandroid backup.

Long story short, if you only flash via recovery and not via fastboot etc. you should be fine.

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  • I would add that, even via bootloader (fastboot), you can replace a rom as, before flashing, any tool erases everything in the system partition. – maxpesa Jan 9 '15 at 12:53
  • Not if flashing the bootloader via fastboot. Then I assume it could potentially wreck the ability to boot the other nandroid backup? – dthomasen Jan 9 '15 at 12:55
  • Wait, one thing is flashing a rom, another is flashing a bootloader – maxpesa Jan 9 '15 at 12:58
  • But a firmware could potentially update the bootloader too? Depending on what's bundled in the firmware? – dthomasen Jan 9 '15 at 12:59
  • Well, basically yes, but messing up creating a new bootloader is not so easy, and most of the users would never use it as it is a common rule to flash a new rom in recovery, nobody would download it – maxpesa Jan 9 '15 at 13:07

I don't agree with the other posters and would say: "in theory yes!". The eMMC of today's phones is partitioned in a lot of partitions. For instance, the Nexus 4 has around 25 partitions. When you install a ROM, it typically only touches system, recovery, userdata, internal sd (if on separate partition), cache and boot. But since the ROM has full root access, it could write to just any partition and e.g. even manipulate your modem stack.

In practice, I didn't hear about a ROM which attempted that. And I if a ROM contains malicious code, it will only reside in system, boot or recovery.

My advice to be sure: before flashing, dump all partitions and compute their checksums so you can see which were modified by the ROM.

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