I agree with most everyone that it's most likely your little brother.
Within the first year my sister started playing WoW (she was 10), she had an internet boyfriend and was looking at porn sites out of curiosity. AND I didn't think she'd do it either, but... there was definite proof. My mom banned her, and I believe it was November... my sister (she's 14 now) started playing WoW again. AGAIN with an internet BF, and some other kid in RL she barely knew, she was sexting both of them. I'm 22, and I don't even sext!
Talk about being traumatized. I don't hold it past younger teens, and kids to look at crap like that anymore.