MALICIOUS URL BLOCKED.....keeps popping up and unable to remove

Since downloading a mp3 file yesterday (converted a YouTube video to mp3, I know i shouldn’t have) I keep getting popups from Avast just like the image I attached, and they will not go away. I have ran a full system scan and 15 files were infected and I deleted them. I am still getting these popups, however, and I got advice from a friend saying it could be a possible rootkit. How can I get rid of this?

This needs further analysis by a malware removal specialist:
Go to this topic http://forum.avast.com/index.php?topic=53253.0 for information on Logs to assist in cleaning malware. Use the information about getting and using the tools and start your own new topic and attach the logs here, not in the LOGS topic.

There is a possible MBR infection there, please follow the steps in the thread and ensure that aswMBR is run if it fails let me know