Legal for HR?

I had a couple interviews with this company and then thought I was out of contention, but they emailed me to ask for a background check authorization. I found it a very odd request. At my current company, we don't ask for that until after the offer has been extended and accepted. So I called and spoke with the Hiring Mgr (who is also HR), because I wanted to know the next steps: have they narrowed down the field? have they determined salary and work hours?Basically I wanted to know if it was worth it to give them my personal information. The Hiring Mgr played coy as if she didn't know the pay and the work hours were still in flux. At that point I was curious to know what the end would be. Are they just stringing me along as a 2nd or 3rd choice in case others fell through? Am I being hired and they just have a backward way of onboarding? Well, I still don't know. The date I was told I'd hear something has come and gone. I'll contact them, probably tomorrow, because I really doubt now if I want this job. But what I'd like to know is this: Is it legal for them to get my personal info (SSN, DL, address, DOB) BEFORE I get an offer of employment and accept?? I feel sorta like I might soon be an identity theft victim (paranoia setting in). It's a reputable company, but still. Does anyone know if this is "normal"?