RESPONSE: It is clear, based on the teaching of pre-Vatican II theologians regarding hearing Mass over the radio or television, that one could not fulfill his Sunday obligation by viewing a Mass broadcast over the internet. The law requires physical presence at the Holy Sacrifice, or at least being part of a group that is actually present (in the case of a congregation so large, for example, that it spills out beyond the doors of the church into the street).
So, if you were able to be physically present at Mass under the usual conditions on a Sunday or a Holy Day, you would be obliged to go to it. You could not choose instead to remain at home glued to your computer— or indeed, to remain in the church parking lot, hovering over your I-Phone — and still fulfill your duty to assist at Mass.
Thus the question of the obligation.
However, the spiritual benefit of a broadcast Mass is another matter — you can indeed benefit from it. This is clear from the comment of Fr. Francis Connell, a well-known moral theologian at Catholic University in the 1950s, who addressed the question of hearing Mass over the radio:
“One may participate in the benefits of the Mass without being actually present — namely, by directing one’s intention and devotion to the sacred rite. By hearing Mass over the radio one can certainly foster his devotion, and thus profit considerably from the offering of the Holy Sacrifice. Indeed, it could happen that one who participates in the Holy Sacrifice in this manner will gain much more benefit than many of those who are actually present.” (Father Connell Answers Moral Questions [Washington: CUA 1959] 75–6)
So, in these days when true Masses offered by real priests are few and far between, Catholics can at least have the consolation of knowing that a facet of modern technology so often used for evil can also be used to foster their own devotion — and indeed, to bring to them the benefits of a true Mass, wherever it is offered.