Adware / Redirects on iOS - iPad 2

I've recently needed to download a number of pdf documents from what I believe to be legitimate safe websites. However, on re-powering my iPad it appears at a similar time new tabs were opened in Safari to porn sites. It has all the indications of adware (although this is usually confined to a PC). As some of you might be aware it is fairly easy to create a javascript / Jquery redirect in a pages code with a delayed trigger if you so desire. It hasn't happened again would I be looking at a page issue or a deeper virus adware concern, or are there any known threats out there. It is notable that I recently restored a virus littered HDD from a PC although Im unsure whether a virus would be cross transferable between systems.