Q: iTunes account possibly hacked

Okay, a few months ago the credit card associated with my iTunes account got hacked and someone tried to charge $6000 on it. I was issued a new card and actually changed my iTunes account to a totally different card. Well, recently that card was hacked as well. When I got the replacement card just now I went to my iTunes account to put in the new credit card info and there was a red box there that said "your account was recently accessed from a different computer". Does that mean that my iTunes account was hacked and that's why my credit cards were too? There was no way to see what computer accessed my iTunes account.

What are the recommendations here? Should I change my apple id password? Is it difficult? My apple id is associated with my macbook pro, my ipad, and mine and my wife's iphones. What problems will I have to deal with? Thanks for any help.