Identity been stolen, my friend needs to froze his credit

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2 weeks ago, my friend received a letter, which stated that his credit card application is already approval. He scratched his head, and he had no idea when and how he get this visa card approved. He called and try to find out what is going on. Obviously, someone stole his social security number, but where and how? A week later, 2 other credit cards application also notified him. The best advise me and another friend to give him is to froze his credit, so no one can apply for another card again. Besides it, notify the 3 credit bureau and keep eyes on monitor the activities. Isn't that scary? Identity theft would done so much harm on it.