Is it normal for someone to post pornography on my account?
A few hours ago, I checked my email and an anon on tumblr asked me if I really posted something. I didn't understand what they meant so I went on my tumblr and looked through my posts and to my horror I found that someone had posted tasteless pornography on my account! The post said something about "helping my sister" and showed a woman bent over with her panties down while she opened her butt checks and showed her anus and part of her vulva! I immediately deleted it and checked through the rest of my posts. To my disgust I found 4-5 more of these photos.
I don't know how this happened. I've considered that my computer might have a virus, but it shouldn't. Another thing I've considered is that maybe someone somehow managed to hack into my account. If that's the case I don't know why or how they did it. I don't give out my passwords and I do my best to be polite to people on the internet so, I can't see why anyone would have a grudge against me. I'm baffled and I'm shaken up over this. I'm worried that whoever did this might do it again or worse might try to hack into my account on here. In my panic, I've even considered deleting my blog but I don't want to have to do that.
Is it normal that this happened?