They called it the Bob and Betty Beyster Bubbler.

Yet a recent unauthorized hot tub installation had nothing to do with the philanthropic couple who recently donated $15 million to the University of Michigan and had the Computer Science Engineering building named after them.

Instead, it had everything to do with a group of mischievous students that decided to pull a prank by installing a hot tub on the CSE building's roof Saturday. And just as it appeared, the hot tub mysteriously disappeared on Monday night.

"People were kind of flabbergasted," CSE spokesman Steven Crang said of the hot tub, which had a wave of visitors Sunday and Monday. "It was obviously unexpected. It was pretty creative and now it's gone. It left a buzz in its wake."

Crang said the group of students responsible is still a mystery.

"It's apparently people who are close to the department because they were able to gain access to the building and install the tub," Crang said, adding that the installation was likely difficult. "The thing that intrigued everyone was that it was on the fourth-floor balcony. It’s a large hot tub and the doors that lead out to the balcony are not real big, so they had to do some work to get it out there."

The hot tub, first reported by The Michigan Daily, sparked a wave of conversation between U-M students on social media, including a thread on Reddit.

"I am in the dude (Duderstadt building) right now, will walk over and check it out here in a few minutes and report back," Reddit contributor fuzzball90 wrote when word of the hot tub first appeared online, later reporting: "It's legit. Working hot tub."

"Can ... can I study in it? I'm not CSE," asked another contributor.

"I don't see why not. I spent an hour in there earlier and I'm Mechanical," fuzzball90 responded.

Images of the hot tub appeared on imgur. That gallery has nearly 144,000 views.

So what did Bob and Betty Beyster think of it?

"They found it amusing," Crang said with a laugh.