We have been having an issue in that Avast Free virus protection has been blocking all the sites in a multisite of ours.
See the forum post https://forum.avast.com/index.php?topic=177897.msg1260467#msg1260467
Now correct me if I am wrong but the code that appears to have caused this is from domain mapping.
If this is actually what happened I'm concerned that it might happen in other sites.
Can you give me some feedback. Has this occurred elsewhere. What can I do to stop it happening again?