Arthur Cabot: Now what does this say about the state of our country, hmm? I mean have you got any insight as to why a bright boy like this would jeopardize the lives of millions? Nigan: No sir. He says he does this sort of thing for fun.
Lynn Lambretta in Bodacious Space Pirates. She was arrested for it when she was in middle school. In high school, she uses her leet skills to foil a pirate attack.
Kazari Uiharu in To Aru Kagaku no Railgun. In the hacker underground, she goes by the pseudonym "Goalkeeper", and is highly respected.
Kululu from Keroro Gunsou. He “could” drain all information from the internet and singlehandedly take over earth, but he seems more interested in causing mischief and making softcore porn.
Marvel UK introduced Adam Reynolds for one of their Transformers Generation 1 annuals. He was attempting to find out how much money was in a friend's bank account to win a bet, but managed to accidentally hack into the Decepticons' data files. Which is the equivalent of walking to the bank and ending up in the secret military lab in the middle of the ocean.
An issue of Spider Man Family had a couple of kids looking for the next big game stumble into one of Stark Industries' files. What they thought was an awesome game turned out to be a program devised by Howard Stark dating back to World War II to protect America from the Nazis. Both Spidey and Iron Man had to destroy the robots that were activated and Tony (as Iron Man) made sure the boys knew they were in trouble.
Aram Fingal (played by Raul Julia) in the Made-for-TV MovieOverdrawn at the Memory Bank, at least initially. He kicks off the film's plot by spending his work hours "scrolling up cinemas" at the office, but once his consciousness is placed in the HX368 supercomputer (long story) his shenanigans end up creating severe weather disasters all over the world, causing billions in property damage to the Evil Corporation that he works for.
Stanley Jobson in Swordfish. Arguably Deconstructed - he's got the requisite madskillz and moral compass, but this just means The Government is that much more smug when they catch up with him and punish him for his actions: destroying the FBI Carnivore program was actually praised by enough of the public to force them to parole him away from computers instead of giving him a prison sentence. But, when his alcoholic wife divorces him due to him losing his job, they have a judge award her with their daughter even after she marries the porn king she works for. The FBI even brags about how his daughter will end up "a fluffer in her new daddy's videos" as punishment for him screwing up their ability to read every American's email.
Tony Stark, AKA Iron Man. The guy effortlessly hacks a live senate broadcast and several military satellites just to prove a point. He also has a tendency to hack other people's sound systems to play appropriate music for his dramatic entrances.
Gwendolen from The Last Dragon Chronicles easily fits this trope. And what makes it all the more awesome? She's an 'inanimate' dragon figurine.
The three guys who make up "The Smoking Gnu" in Going Postal. This being the Discworld, they hack the semaphore-driven "clacks" network, which is a telecommunications system, but without the electricity.
The Smoking Gnu are more Playful Hackers turned Crackers, as they use tricks they originally discovered while playing around with the mechanisms to work out how to physically destroy the entire network of clacks with a message. It should be noted that they don't actually enact that plan..
As of The Science of Discworld II, Hex has also joined the Playful Hacker ranks, as it's hooked up to the semaphore network, has cracked their operations codes, and can slip messages onto the network for free, passing them off as internal signalling. So far as we know, it's only done this to save the UU faculty the expense of sending c-mail messages.
Cadel Darkkon functions as this in Catherine Jinks' Evil Genius Trilogy. Slightly subverted, as in the first book Cadel was closer to a cracker, given his initially amoral nature- until he met one of the victims of his destructive schemes.
Most of the members of Genius Squad are playful hackers, though Hamish Primrose would be the best example.
(Smokin') Jay Gridley from Tom Clancy's Net Force.
One of the Hats worn by Bothans is that of the hacker (the others are vicious backstabbing politician and spy). The Bothan pilot who makes it into Wraith Squadron is a bit malicious but more or less Playful.
Ghent, from The Thrawn Trilogy and later the Hand Of Thrawn duology, is one of these. He is very good at hacking and does so for the sheer pleasure of it. He also has blue hair.
Ender in Ender's Game, who cracks into the desk system in the Battle School and figures out how to send messages under other student's names, while preventing other students from using his name. This is only used for pranks, of course, as Ender is only six years old at the time.
And it's implied that the computer system is deliberately set up to allow and encourage this sort of competition/play/hacking.
In Vernor Vinge's cult-classic novella, "True Names", most of the members of The Cabal fall under both this and The Cracker. They're all out to have fun, and to gain bragging rights, but they're all also criminals. Of course, some of them are more criminal than others, so we do eventually get the classic Playful Hacker vs The Cracker showdown.
Live Action TV
Directly inspired by WarGames, Richie Adler from the short-lived series Whiz Kids. Richie even acknowledges some similarities but says that he, as opposed to Lightman, is a genius. But then, his computer RALF is also a Magical Computer.
Mac on Veronica Mars: a Playful Hacker with the tendency toward being a bit of a Cracker. She's helpful to Veronica in solving cases, but as Veronica herself operates outside the law for profit, Mac does the same.
B.B. from Metal Gear Acid 2. Instead of being childlike, though, he was — literally — a child (age negotiable, but still in Elementary School). He played comic relief throught the game, culminating in him copying Psychic Powers from a boss and hypnotising the President of the United States — totally ridiculous, but it worked because it was funny.
One of Otacon's talents in Metal Gear Solid to boot. He clearly takes great pleasure in hacking into his boss's files during the third act, and cheerfully remarks that the hacker label describes him "pretty well".
In Deus Ex, Silhouette's claim to fame is hacking a Superbowl broadcast and inserting anti-UN propaganda.
Hammer from Xenosaga is said to have top-notch hacking skills, so much so that he's been head hunted by the top corporations of that 'Verse. The database states that in his youth, he hacked into a criminal database, and that his current employers, the Kukai Foundation, protected him from them.
The "hacker" from the original System Shock. The story gets kicked off when he gets caught.
Between the events of Mass Effect 2 and Mass Effect 3, Cerberus attempts to regain control of the Normandy after Shepard cuts off ties with them. Unshackled EDI's response? Spamming the Cerberus hackers with seven zettabytes of porn...from Joker's Porn Stash.
The crew of the Normandy is joined in Mass Effect 3 by Samantha Traynor, who among other things enjoys strategy games and manages to impress EDI with her ability to sift through data to track a Cerberus shuttle.
Shinji Naruse, a childish and Tsundere high school student in Lux-Pain is a gifted hacker who manages to break into the files of the main character's secret organization... because he can. He ends up facing the Cool and Unusual Punishment of having doctored (and dirty) photos of him posted on the internet by said organization.
Yukabacera from Iji is apparently one, at least according to his hidden character pages on Daniel Remar's official site. He'll hack one of the station terminals in the room just to code a video game for other people's enjoyment. (This game can actually be played in Sector 6, the sector where Yukabacera is hiding)
You in Uplink, if you so choose. Hack someone's academic record and give him nonsense degrees! Change their status from "Single" to "Married" or even to "Deceased" for no particular reason. Hack into the bank and steal exactly one creditjust because you can.
Jack from Gunnerkrigg Court has made a hobby of hacking his dorm's security system so he can sneak out and explore the Court after-hours.
Yuri from Spacetrawler. She can open or lock any door on the ship, and she's already read a number of files that the captain doesn't want anyone to see.
Vauxhall from A Tale Of Fiction fits the bill. He seems to know more about the tyrannical DUF than almost anybody else from his hacking activities and works against them, but otherwise is a harmless and funny (if porn-addicted) guy.
Sollux Captor and Alpha Roxy Lalonde from Homestuck. Sollux is a better example of the trope - he once managed to hook Terezi into contact with Doc Scratch. Who doesn't have an account on the chat client she uses. And uses a TYPEWRITER. AND LIVES ON THE MOON.
Zaboo occasionally ventures into this territory in The Guild.
Freddie from Behind The Veil fits pretty well, despite being born a wolf. Mike Hoffman also has shades of this.
Mysterious Mr. M of LIS_DEAD can infiltrate deep into a secret organization, barely escape by the skin of his wits, and code a nice little Tetris minigame when he gets home, snarking all the while
Occasionally in Code Lyoko, when Jérémie is testing a new program. However, he normally uses the Supercomputer to escape from sticky situations. For example, when the school staff tries to find out about William's disappearance and Jérémie uses his voice synthesizer.
Mouse from ReBoot. Even weirder when you consider she actually lives inside a computer. One could guess she's some sort of hacking software (just like how Bob is essentially a computer security suite).
By the bytes, it all makes sense! Enzo is some edutainment software, whilst Fong is the kernel.
Given Mouse and Bob's past "association", she's more likely a tweaking app.
Once in Robot Chicken the nerd accidentally nuked Canada while looking for cheat codes, he was sent to Guantanamo Bay and waterboarded until he told them where Mordor was.
While he's more of a Technopath, Doc Hartford of the Galaxy Rangers never lacks for a sense of humor, and is more likely to try and sweet-talk or trick an AI than overpower it.
Many computer geeks feel themselves to be exactly this. This flavor of hacker refer to themselves as "White Hats" (at least, those who just look for exploitations and inform the authors of the software). Word of advice — don't screw with government pages, though. It seems any sort of hacker does time after vandalizing a government page.
The trick is to vandalize some other government's page than your own. (Just kidding, never do anything like that — honest!)
A popular April Fool's day joke on websites is to alter the front page to make it look like the site has fallen victim to internet vandals. Fark.com is (apparently) particularly vulnerable to guinea pigs, or as they call themselves, TEH PIGZ.
Lulz Security/Antisec members consider themselves to be these, as evidenced by their snarky, meme-laden press releases.
The NSA has their own department of white hat hackers that constantly test their own systems.
M.I.T. has a long tradition of "hacks" dating back long before computers were available, with their own website dedicated to tracking them, as well as at least five books — one of which is published by the university's museum press.