The screensaver uses thousands of computers worldwide to drain the available bandwidth on spam sites, thereby making the use of spam less profitable. Lycos' screen saver "pulls its punches" however, so as to not DDOS the sites in question.
Yes, it's vigilante, and yes, it isn't the ideal solution... however, it's an idea that open source developers are bound to take even further and make significant improvements to, and I tend to believe that encouraging a lot of bright people to think up ways to hurt spammers is noble cause. Expect the inevitable open source solutions to be a whole lot more effective, clever, and generally less throttled than Lycos' attempts. In the meantime, using the screensaver is a little bit of payback and is worth supporting for the time being.
Technically, the software is only supposed to be available to Lycos' European users, but anyone can download and install it. Here are direct links to the software that avoid Lycos' ad pitch.
Direct download for Windows version.
Direct download for MacOS X version.
Direct download for MacOS 9 version.
Expect a fast-paced "running battle" as spammers and Lycos adjust their tactics, and as Open Source developers quickly enter the fray with their own solutions. Should be fun to see what happens. The fallout might be bloody. I guess we'll see...
***Update: Lycos' anti-spam screensaver is programmed in Shockwave Flash, which means that you can run it on a webpage. That means you can open several pages at this link and leave them running all the time, thereby nuking spammers in a quicker, more agressive manner. Excellent! ***