This exception is thrown when an application attempts to perform a networking operation on its main thread. 
Run this sample code:
class RetrieveFeedTask extends AsyncTask<String, Void, RSSFeed> {
    private Exception exception;
    protected RSSFeed doInBackground(String... urls) {
        try {
            URL url = new URL(urls[0]);
            SAXParserFactory factory = SAXParserFactory.newInstance();
            SAXParser parser = factory.newSAXParser();
            XMLReader xmlreader = parser.getXMLReader();
            RssHandler theRSSHandler = new RssHandler();
            xmlreader.setContentHandler(theRSSHandler);
            InputSource is = new InputSource(url.openStream());
            xmlreader.parse(is);
            return theRSSHandler.getFeed();
        } catch (Exception e) {
            this.exception = e;
            return null;
        } finally {
            is.close();
        }
    }
    protected void onPostExecute(RSSFeed feed) {
        // TODO: check this.exception
        // TODO: do something with the feed
    }
}