Peter is writing about this excerpt from The Code Book.

A variation on the Trojan horse is a brand-new piece of encryption software that seems secure, but which actually contains a backdoor, something that allows its designers to decrypt everybody's messages. In 1998, a report by Wayne Madsen revealed that the Swiss cryptographic company Crypto AG had built backdoors into some of its products, and had provided the U.S. Government with details of how to exploit these backdoors. As a result, America was able to read the communications of several countries.

Which of Peter’s lines shows that he is using personal experience to understand the reading?

Hidden messages can be shared through a backdoor in encryption software. It reminds me of the way I leave my kitchen door open so the cat can come in.
Hidden messages can be shared through a backdoor in encryption software. The author gives an example of this software helping the government.
A Trojan horse is a type of encryption software, but as the author explains, it is not always 100 percent secure.
A Trojan horse is a type of encryption software, which reminds me of Greek mythology.