What version of Avast are you using? What is your OS?

You may want to read this http://www.techsupportforum.com/forums/f112/solved-woah-woah-woah-some-werid-program-installed-on-my-computer-352654.html to learn how this software got installed on your machine and how to uninstall it. It is common for the scans you mentioned to come out clean.

Clean all your temporary Internet files with something like CCleaner http://www.piriform.com/ccleaner/builds - scroll down and there is a Slim version available with no toolbars. I suggest doing this after every time you finish going on the Internet now, then in the future.

What type of scan did you run on Avast (Quick, Full, Custom, Boot) and were your definitions up to date? If you did not already run a Boot-time scan, please do so to be on the safe side.

Run the uninstaller from the link I posted above, then reboot your machine.

Keep your Avast and MBAM definitions up to date. You may also want to search for this software > Advanced Search and type in Pando to see if anything comes up. If it does, uninstall it with Revo. From the link above, the user with this problem used Revo to uninstall http://download.cnet.com/Revo-Uninstaller/3000-2096_4-10687648.html, and this is a good program (except for uninstalling security software) to get rid of remnants. Reboot after uninstalling.

Make sure your Avast P2P Shield is activated and at default for sensitivity.

Let us know how you do and if you have any questions. Thank you.