WELCOME TO THE PENTAGON is a quote from a 2007 article on RFSHQ titled The Club Penguin Hacking Prank.
The prank, performed by Dracophile and squirrel007, was centered on fooling a random annoyance of squirrel007 into thinking that he had created a Club Penguin hacking tool that operated via AOL Messenger. The victim, batista 1026, spoke with squirrel007 about how to use the software while feeding Dracophile (posing as "CPHackBot") requested information and other nonsense that squirrel007 told him to copy and paste.
The Windows 98-operated bot purposefully messed up by "giving" out the wrong items, returning error messages, or opening Windows Solitaire instead. At one point CPHackBot "hacks" into the Pentagon, displaying an array of numbers and symbols with the phrase "WELCOME TO THE PENTAGON" and after an unsuccessful attempt at logging in messages are displayed claiming that the person controlling the hacking bot will be traced and arrested for cybercrimes.
The Club Penguin Hacking Prank was one of a few Club Penguin-based articles on RFSHQ but like the others did not garner immediate attention. It would only be appreciated several months after its initial posting when the phrase "WELCOME TO THE PENTAGON" would become a recurring joke generally used to reference hackers in Club Penguin or as a tongue-in-cheek way to address computer connectivity issues. While the victim of the hacking prank was dumb enough to provide the full login information of his account, his account was never touched and he later vanished from the community.
The meme has mostly died out but as recently as the Forum Days of Doom of 2010 the phrase has seen some usage by veteran MCCP users.