GIMPS

The Great Internet Mersenne Prime Search. A distributed computing effort to find really big prime numbers. Just recently, a GIMPS user was awarded $50,000 by the EFF for finding a 2,098,960 digit prime number: (2^6,972,593)-1.

GIMPS, located at http://www.mersenne.org/prime.htm, is the largest of several efforts to find prime numbers using idle time on ordinary home PCs.

GIMPS provides free software written in highly optimized assembly language. Using this software, individuals who own a Pentium-class PC with any major operating system can search for prime numbers with millions of digits. It is interesting to note that, despite the fact that each candidate number can take weeks or months to test, there is a larger chance of succeeding in a given time then in distributed.net or SETI@home

The clients are Prime95 and mprime, and are written by George Woltman.

GIMPS has found 4 more primes.

On November 14, 2001, the Mersenne prime M_13,466,917 (2^13,466,917-1) was discovered.
On November 17, 2003, the Mersenne prime M_20,996,011 (2^20,996,011-1) was discovered.
On May 15, 2004, the Mersenne prime M_24,036,583 (2^24,036,583-1) was discovered.
And on February 18, 2005, the Mersenne prime M_25,964,951 (2^25,964,951-1) was discovered. It has 7,816,230 decimal digits.

The next EFF prize is $100,000 for a minimum 10,000,000 digit prime.