If you know what Infinity Mode is, skip to the second paragraph. If not, read on... 

Infinity Mode is unlocked after beating Overtime Mode which is unlocked by playing 72 Hour Mode and getting the best ending. Infinity Mode is basically a "Survivor Mode" in which the entire zombie-infested mall is open to you. Your health is constantly depleting, and the only way to restore it is by eating food. Since food is so valuable in this mode, it is also very scarce. There is an extremely limited supply just lying around the mall. The only way you can survive for more than a day is by defeating the randomly spawning bosses that appear from time to time. They'll drop a supply box, and you'll be set for awhile until you find someone else to fight. By now you should know that finding a safe place to hide, setting the controller down, and letting the 360 run is not an option. You have to constantly be on the hunt for more food. Also, there are no save opportunities. The only way to take a break or sleep is to pause the game. There are two achievements related to this mode. 5 Day Survivor unlocks the Laser Sword, and 7 Day Survivor unlocks the "Arthur's Boxers" clothing item.

I hadn't played my 360 in a long time. Ever since the FormID Reference Bug ruined Oblivion, I've been playing my SNES and DS a lot more. But the new South Park episode got me in the mood to play Dead Rising. (They spoofed Dawn of the Dead.) I never gave Infinty Mode a chance before, so I started playing to see what it was all about. Well, I found it fun. The whole survival aspect was engaging and forced you to actively play the entire time. I kept playing until I survived for a full day. I thought, "That wasn't so bad. It took awhile but it was pretty easy combat-wise. I might as well keep going." So I kept going. I told myself that I would play until I survived for 5 days, unlocked the Laser Sword, and got the 5 Day Survivor Achievement. By the time I did that, I had been playing for hours. Over 10 hours to be more specific. I then thought, "Ok, I've played for over 10 hours, and there's no way I'll ever do this again. The only way I'll ever get the 7 Day Survivor Achievement is if I keep going." So I kept going, again. More than 4 hours later, when I finally reached the 7 day mark, I had some food left over to survive awhile longer, but it was 7:09 a.m. and I needed some sleep. So I marched myself into a crowd of zombies and let them eat me alive. And that's how I spent my Friday night. My girlfriend said that it was nothing to be proud of. But I know better. GO ME!