Why is my Macbook's battery bulging?

Hello Everyone,

I own a 13-inch Macbook (Black) (purchased it in 2007), currently running Mac Snow Leopard.

For about a month or so, I began to have problems with my trackpad; going crazy, click on hold, button getting stuck. However, I never thought it was my battery that was causing the problem. I noticed it's now bulging. If I remember correctly, when I first purchased my Macbook, I did had a little trouble getting it attached to my computer. But I never bother being concerned about it until now...

A little too late, I know. But I heard 2007 Macbooks had battery infection problems (I searched it up.). So this isn't normal for a battery to bulge? (I don't know much about computer batteries.) And since my warranty was up last year, am I unable to get a replacement free of charge?

I also purchased this laptop at COMPUSA, but it went out of business, so I'm running out luck here.

So I guess my main question is the replacement and the *cause of the bulge*. I'm not using the battery after hearing it's dangerous to be using it. I can't believe my computer was at risk for the last 3 years without noticing. So much for that.

Thank you for your time.