Hi there. I don't want to upset you or offend you in anyway but I'm afraid that I have some bad news to tell you ASAP as it has become quite a big concern for everyone on dA. I found out from this journal here:
[link] that someone has been going around stealing artworks on dA and been uploading them on this website:
[link]And if you type your dA username in the search box, you'll find some of your artworks posted there. If you go to the journal I linked above first of all, there are few people you can contact to inform them of copyright infringement of your artworks. I apologise if I'm babbling too much but I just wanted to let you know so that justice can be brought to these art thieves.