In the watery depths of cybersite Aquari-yum, the kids and Hacker go in search of a giant cyber-slug, who feeds on pure energy. The kids and Digit travel underwater in two separate vessels, but Hacker has a listening device that taps into their communications system, allowing him to overhear their plans and track every move they make. The kids outsmart Hacker by devising a series of codes so they can send messages back and forth in secret — even though Hacker can hear what they’re saying. Hacker surprises everyone by perfectly understanding and taunting Matt in Pig Latin by saying "Iyay'llay oday oremay anthay arescay youyay ifyay youyay ytray otay opstay emay" ("I'll do more than scare you if you try to stop me") revealing that he knows Pig Latin. The kids first try a code that uses word numbers, line numbers, and page numbers from Digit's cookbook (which wasn't exactly a best seller) but like Pig Latin, Hacker is able to understand them, so they device a new code that uses photos and postcards from Digit's album that have been labeled with numbers that the kids radio and decode by turning the number-sides to reveal the message. But unless the kids can reach the slug first, Hacker will use the slug to attack Motherboard’s circuitry and disable her once and for all!
- Math topic: "Codename: Icky" focuses on codes with rules.
- For Real Segment: "Harry's Cracked Code" - Harry and his friend, Julio, have found an ancient Viking alphabet (actually very similar to Cirth in Lord of the Rings) to send coded messages to each other. For fun, Julio uses the code to invite Harry to a special event. Harry decodes part of Julio's invitation, then stops when he thinks he knows the rest. So, why is he the only one who shows up at Julio's in costume Saturday night?
- Trivia: Cryptographers (someone who studies cryptography) consider Pig Latin to be a very weak encryption method, even more so than Caesarian ciphers, as first of all the only rules to Pig Latin is that you take the first sound of each word in the message put at the end and add "ay" and you simply decode Pig Latin by reversing the process— drop the "a" sound and put the last sound first. Not only is this very weak method of encryption, but the second biggest flaw and weakness of Pig Latin is that it also becomes very difficult to encrypt very large messages, so Pig Latin is best used for short messages no bigger than just a few words— anything bigger than that and it becomes very difficult and may require a cheat sheet.
- Main article: Codename: Icky/Transcript