Is Ad-hijacking or Ad-injecting legal? Or just frowned upon?
pbhjpbhj: In most cases I'd guess that it's unauthorised modification of a copyright work. The presentation of a blog for example is formed by design with the adverts - they constitute a part of the work as a whole, removal of the adverts without license would be copyright infringement as it's formation of a "derivative work".Compare a newsagent (ISP) selling a magazine (website). If the newsagent censors any adverts for a competitor in that magazine by pasting over their own advert before selling it on then they've modified the magazine ; without a license this is copyright infringement.