United Devices is running the effort. All you have to do is download their closed-source, restrictive-licensed client program and install it on your PC (you also have to agree to their website license to even download the program, of course). You take all risks of installing the program - if the program deletes every file on your computer, too bad. If it downloads some kiddie porn and emails email@example.com confessing to the crime, too bad. And I hope you don't pay for bandwidth by the byte, because their main commercial effort seems to be stress-testing websites for Exodus. You do read those license agreements, don't you?
Here's UD's business model in a nutshell:
"Get people to give us computing power and bandwidth for free and sell it to other people."
A nice gig, if you can get it. UD's primary business is selling computing cycles to corporations. As it turns out, they were having a hard time with the first part of the business model, so they came up with a scheme to get people to install their client: we'll do philanthropic work! And what could be more philanthropic than curing cancer?
Who else can we get on board? How about Intel? They're always willing to sponsor anything that promises to burn a lot of CPU cycles. In fact, they're willing to put up a disgusting website that totally misuses the term "peer-to-peer" to achieve an alliterative buzzphrase.
So, the stage is set. Now, read through the site that UD set up for this effort. Try to find in it any mention of anything other than philanthropy and cancer curing. You won't be able to. Why, you might even start to believe all this client does is work on curing cancer. Now go back to UD's main web site and read through it, noting how your computer will be sold to any corporation willing to pay for it. The task your computer runs is determined by UD, not by you.
Even the cancer research isn't philanthropic in the usual sense. Say that your machine discovers the drug that cures cancer. Who benefits? Well, Oxford University will patent it and sell the rights to produce it at some extortionate price, the name-brand drug will be hideously expensive, and 20 years later when the patent expires, the world will be able to afford cancer cures - shame about all those people that died in the meantime.
That's "philanthropy" in the digital age - agreeing to a restrictive license and running a program which can do anything it wants with your computer system or network including destroying it or committing crimes with it or running up your phone bill, all the while doing free work for a for-profit corporation so that a drug company can get a patent on a life-saving drug and charge outrageous prices to pay back the "research costs".
I think I'll stick with xscreensaver.