Its creator remained anonymous.

But for political strategists, ad experts, even journalists, the ad presents a series of other fundamental unknowns.

- How will Web content outside the control of campaigns affect voters?

- How should campaigns react to anonymous but highly viewed attacks?

- When is Web content, no matter how provocative, newsworthy?

As the Internet looks more and more like an electronic community, politicians are increasingly devoting resources to their Web sites, planting themselves in electronic gathering places such as Facebook.com and MySpace.com and posting their videos on YouTube.

With some exceptions, however, what draws viewers is content that politicians don't control. A video clip of former Sen. John Edwards combing his hair to the dubbed-in tune of "I Feel Pretty" has drawn more than 150,000 views. A clip of Clinton singing a slightly off-key version of the Star-Spangled Banner has drawn more than 1 million views.

What's more, Internet content does not have to meet the strict reporting standards that television and radio ads must observe. That makes the Web the medium of choice for stealthy tactics by partisans operating outside the campaigns.

For candidates caught in the crosshairs, one way to respond is to brush it off, preferably with humor.

Asked about the Macintosh video on Tuesday, Clinton said: "I'm just happy if it's taking attention away from my singing. My singing was bad enough. I'm just happy that nobody is tuning in to that."