SwiftOnSecurity says the fake extension was created by a "fraudulent developer who clones popular name and spams keywords." Indeed, it's pretty hard to tell that it's fake, since its developer's name is "Adblock Plus," and it has a considerable number of reviews. According to one of the fake Adblock's reviewers, he started getting invasive ads that open lots of tabs after he installed it. Unfortunately, it's unclear what else it can do or if it has even more detrimental effects that we still don't know of. We asked Google if it has unearthed anything about the fraudulent extension, but even if we never hear back, it may be best to re-install Adblock Plus if you notice getting random ads after downloading it.
A copycat version of Chrome's AdBlock Plus has been downloaded by thousands people. Google removed the fraudulent extension from the Chrome Web Store after SwiftOnSecurity tweeted about it, but 37,000 had already been tricked by the phoney listing. Users are advised to re-install Adblock Plus if they notice random ads after downloading it.