US hit by massive Internet outage .
A user-generated outage map on DownDetector .com showed that it was down in large cities like San Francisco, Los Angeles, Seattle and Boston .
Confirming the reports in a tweet on its customer care account, Comcast wrote, "Some customers are having issues with their XFINITY Internet service . We apologize & appreciate your patience while we work to fix ."
As of 12:40pm Pacific, Comcast tweeted that the issues should now be fixed . (ANI)