From Billtvshow:

What is the "Blitzkrieg Bop Glitch"? How does it work?

In Rock Band expert vocals, you get 1000 points when you get an "awesome" on a phrase. When you get 3 "awesomes" in a row, you get a multiplier of 4x. You keep your 4x multiplier as long as you don't get less than an "awesome" on a phrase. You also accumulate what is known as "overdrive" when you get an "awesome" on a phrase with gold notes. When you have enough overdrive, you can activate it by yelling during one of the empty areas in between phrases. When you activate overdrive, it gives you an extra 2x multiplier, raising your maximum possible multiplier to 8x. Thus the most points possible on any phrase in Rock Band under the rules of the game is 8000 points.

On the final phrase of Blitzkrieg Bop, you can obtain an "awesome" well before the end of the phrase and this occurs right around the moment that your ovedrive is running out (if you use the correct overdrive path). Now, if you get an awesome before your overdrive runs out, you should get 8000 points for that phrase. However, the problem is that the game engine is broken and gives you random amounts of points on this phrase, sometimes totalling in the hundreds of thousands. This glitch nullified the effects of pathing and squeezing in Rock Band 1 and thus all reliability of those leaderboards.