Has anyone else's tablet been rootkit infected over wifi?

[minimobile]

I thought that Oldboot/Moubad firmware infections were limited to tablets that had been purposely flashed with updates from an SD card. My EKEN A46H tablet seems to have a permanent rootkit infection, but has never been reflashed. I did a factory reset, data delete/format. The tablet behaved for about 30 minutes, and then again began streaming full screen video clip ads which could not be dismissed. It appears a rootkit remained that reloaded the malware, and connected to its servers in that 30 minutes. I bought the tablet new, and it behaved for three months. I always used Google Play to download. I don't play video games, or have Facebook, yada, yada. Just Firefox, youtube and productivity utilities. Unfortunately, EKEN doesn't have firmware available for my model, so I can't reflash it, even if I wanted to. Either the rootkit came with the EKEN, and had a 3 month timer before it went into action, or I got the infection over the internet.
Anyone else seen this problem?