It is possible that the virus was hiding in system restore.
If you right click My Computer / left click Properties / left click system Restore, / put a tick in turn of system restore to all drives / left click apply / left click OK / then run your anti virus again.
to be sure you can also run an online AV scan from here.
After doing this switch system restore back on by taking the tick out of the box.
When you switch system restore of you will lose all your restore points.