It`s not something to do with your Google ad settings is it? I can`t do a link because I`m on Firefox with an adblocker but on IE I have ads and there is something on the RH side about adchoices. That has a little green triangular type arrow thingy and if you click it, it tells you all about it.
It may not cure the problem in your Orchard stewey, although if I pick up a virus, Malwarebytes either quarantines it and tells me what it is, or deletes it. It depends, have you added a new programme or downloaded something dodgy recently? It maybe as 237sj says about adchoices, click on the green arrow.