  The Virasoro groups are a family of central extensions of
$\mathrm{Diff}^+(S^1)$, the group of orientation-preserving diffeomorphisms of
$S^1$, by the circle group $\mathbb T$. We give a novel, geometric construction
of these central extensions using "off-diagonal" differential lifts of the
first Pontryagin class, thus affirmatively answering a question of
Freed-Hopkins.
