I was just talking to this one guy on Yahoo messenger and he said he knows my IP address and my Main IP provider,that he did DOS Command.. something like that while talking to me. He said he can easily hack my computer and know private things about myself,infos,credit cards etc..Like for example I am shopping online, he said he could easily use the account. What should I do now ? Should I change all my passwords ? I am scared.I am using Macbook Pro 15inch by the way if you need this info.. Pls.help.