Sony sent a letter to the U.S. House of Representatives on Wednesday, indicating that they have found a file left behind by the hackers on their systems. The text file left behind carried the name “Anonymous” and the words “We Are Legion”.

The Anonymous name refers to a loosely-organized group of protesters who stage real-world protests coupled with “hactivisim”, an activity including hacking and denial-of-service attacks against large companies. Anonymous typically acts under the banner of free speech or other freedoms, with most attacks staged in response to a specific action.

Anonymous did carry out a number of denial of service attacks against Sony in response to Sony’s lawsuits agains George Hotz. Hotz and others were sued by Sony for jailbreaking the Sony PlayStation 3, hacking its security systems so that unauthorized software could be run on the system. During investigations into the suit, Sony was also given access to IP addresses of people who visited Hotz’s blog, where information about hacking the PS3 was published. The IP addresses were meant to provide information about what jurisdiction would hear the case.

Sony said that investigating the known denial-of-service attack, it found evidence that some hackers had broken into the PlayStation Network servers, compromising 77 million PSN accounts. This discovery was announced on April 26. On Monday May 2, Sony announced that Sony Online Entertainment servers were also the victim of a break-in, and it is here that they found the Anonymous file.

Hackers under the Anonymous name took credit for the denial-of-service attacks in response to the lawsuit against Hotz and the release of IP addresses to Sony. However, Anonymous as a group has not claimed responsibility for the server break-ins.

The security breach reportedly compromised personal data for 24.6 million PSN members, including credit card or banking information for about 20,000 members.

Sony says it will begin to restore services this week, and will offer PSN subscribers a free month subscription of its PlayStation Plus service, including a variety of free downloads.

The announcement comes the day before Microsoft releases its highly-anticipated Live Experience to Xbox 360 users.  The new system will improve interaction among players on the network, introduce player avatars and revitalize the Xbox 360′s interface.  Sony is probably hoping to dispel the common conception that its PSN is inferior to Xbox Live, which seems to be preferred by most regular gamers.

Microsoft is very excited about the new Live Experience, insisting that it represents that future of home entertainment content. “With the New Xbox Experience we will reach the next generation of Xbox owners, 25 million and beyond.” said Don Mattrick, senior VP at Microsoft. “We are at a watershed moment, backed by the largest entertainment brands, with an incredible line up of entertainment unmatched in any industry.”

As Mattrick indicated, Microsoft is approaching 25 million Xbox 360 consoles sold.  Compare that to 35 million sales for the Nintendo Wii, and 17 million for the PS3.  Although the Wii is reaching a wider audience, Microsoft is confident that it can maintain its lead over the PS3 indefinitely.

Needless to say, Microsoft has high hopes for its updates, but insists that the new Live Experience is just the beginning.  Xbox 360 players can judge for themselves tomorrow.  The new Xbox Live Experience update will begin downloading automatically on Wednesday when players sign into Xbox Live.

The new system will offer not only feature films but also full-length television programming available over the PlayStaiton Network.  No official date has been given, but word is that the PS3 will introduce some of these services this summer.