
If the problem remains, then the cause lies deeper, at a browser, settings, or system level. If this clears the problem, then it involves infected code from one of those sites, either stored by the browser or auto-visited upon browser startup. Generally speaking, the first thing to try in such cases is clearing all the browser's cached data and preventing the browser from auto-loading any potentially problematic website code (particularly prior sessions, speed dial selections, or even homepage).
something injected into the download data stream by a less-than-ethical ISP. infected material on a computer/drive that is set to auto-activate along with the browser (malicious files, a hacked command appended to a shortcut, etc). something attached to or called up by the browser upon its own startup (plug-ins, extensions, etc). something embedded within a website's page code which is auto-called each time the browser starts (session tabs, homepage URL, speed dial URLs, etc). something embedded within a browser's own cached data or saved settings (speed dial or homepage material, hijacked search engine, etc). Logic dictates that malware or adware constantly reappearing in a browser can only originate from among the following places: