Gaming Reviews, News, Tips and More.
We may earn a commission from links on this page

That Time A German Hacker Leaked Half-Life 2's Source Code

We may earn a commission from links on this page.

Players have been waiting a while for Valve to release another Half-Life game. It’s taken long enough that it’s easy to forget all the drama that circled Half-Life 2’s development. You know, like a hacker leaking an early version of the game in September 2003, more than a year ahead of its actual release date.

Yes, that actually happened.

Valve started working on Half-Life 2 shortly after the release of the original game in November 1998, which ended with Gordon Freeman saving the day, only to be placed into forced stasis by the mysterious (but handsome) G-Man.


These days, video games are announced years in advance, with publishers slowly teasing out new information about the game as the release date nears. The waits are unbearable. While rumors circled about Half-Life 2, the game wasn’t formally announced until it showed up as a surprise at E3 2003, and Valve said it would arrive only a few short months later, September 2003.

Someone even captured the whole E3 2003 demo:

September 2003 came and went, and Half-Life 2 was nowhere to be found. Valve hadn’t given a reason for the game’s delay yet, nor revealed how far behind it was. (It wouldn’t get released until November 2004, more than a year later.)


But in the midst of September, German hacker Axel Gembe found his way onto Valve’s servers and managed to download the source code for Half-Life 2. Eurogamer published a profile of Gembe a while back, which I recommend reading, as it paints a compelling story of a hardcore fan who messed up badly.

Per the Eurogamer story:

Gembe’s malware crimes, while undeniably exploitative and damaging, were crimes driven by a passion for games rather than profits.

His favourite game of all was Half-Life. In 2003, like so many fans of the series, Gembe was hungry for details about the forthcoming sequel. That’s when he had the idea. If Gembe could hack into Valve’s network, he might be able to find something out about the game nobody else knew yet.

A socially awkward loner who had endured a tough upbringing, he would gain status in the community of gamers he had adopted as his family by offering up such insider information. It was worth a try.

It worked out—for him. Gembe claims he didn’t upload the game’s source code to the Internet, but once it started spreading, it was impossible to stop it.

Valve didn’t take the leak lightly; co-founder Gabe Newell was super pissed. He posted to the company’s message boards looking for help on what happened:

Ever have one of those weeks? This has just not been the best couple of days for me or for Valve.

Yes, the source code that has been posted is the HL-2 source code.

Here is what we know:

1) Starting around 9/11 of this year, someone other than me was accessing my email account. This has been determined by looking at traffic on our email server versus my travel schedule.

2) Shortly afterwards my machine started acting weird (right-clicking on executables would crash explorer). I was unable to find a virus or trojan on my machine, I reformatted my hard drive, and reinstalled.

3) For the next week, there appears to have been suspicious activity on my webmail account.

4) Around 9/19 someone made a copy of the HL-2 source tree.

5) At some point, keystroke recorders got installed on several machines at Valve. Our speculation is that these were done via a buffer overflow in Outlook’s preview pane. This recorder is apparently a customized version of RemoteAnywhere created to infect Valve (at least it hasn’t been seen anywhere else, and isn’t detected by normal virus scanning tools).

6) Periodically for the last year we’ve been the subject of a variety of denial of service attacks targetted at our webservers and at Steam. We don’t know if these are related or independent.

Well, this sucks.

What I’d appreciate is the assistance of the community in tracking this down. I have a special email address for people to send information to, If you have information about the denial of service attacks or the infiltration of our network, please send the details. There are some pretty obvious places to start with the posts and records in IRC, so if you can point us in the right direction, that would be great.

We at Valve have always thought of ourselves as being part of a community, and I can’t imagine a better group of people to help us take care of these problems than this community.


Though some fans were frustrated at Valve’s silence about the Half-Life 2 delay, most rallied around the intrusion and vowed to help out in any way they could:


Newell ended up getting help from an unlikely email source: Gembe himself.

Again, per the Eurogamer piece:

Why did Gembe send that email? “Because I was sorry for what happened,” he says. “I wanted them to know who did this thing, and that my intention was never for things to work out the way they did.”

But that wasn’t all that Gembe was after. The young man saw a way he could create a positive outcome from his crime, both for Valve and himself. In a separate email, he asked if Newell would consider giving him a job.

“I was very naïve back then,” he says. “It was and still is my dream to work for a game development company, so I just asked. I hoped that they could forgive what I had done, mostly because it wasn’t intentional.”


Newell agreed to speak with Gembe, pretending to be interested in having him join Valve’s in-house security team. Gembe took the bait, and was slated to fly out to the US. The moment he touched down, Gembe was to be arrested by the FBI. That didn’t happen, though, because the German government arrested him first. Gembe was then charged with hacking into Valve’s network. It was never proven that Gembe uploaded the source code, but he did admit to infiltrating Valve, which prompted the judge to give him two years probation.

What leaked is sometimes called a beta, but that’s misleading. Valve has never really talked about the leaked version, always referring to it as a theft. It’s unclear what Gembe actually managed to download. It shares elements with the finished version of Half-Life 2 that shipped the following year, but also contains a number of stages, enemies, weapons, and other elements that Valve removed.


This Wikia entry has details on what Valve cut, such as the Combine Guard.


Some pieces, such as the creepy Stalker enemies, eventually made their way into Half-Life 2’s two episodic expansions, as Valve plucked what they still liked.

It’s not often such a raw version of a game is revealed to the public. Theft is terrible, of course, but that part is super interesting. It’s one reason why people have continued to obsess over it, putting together detailed comparison videos:

Some modders have even tried resurrecting the cut material, which best surfaced in the once-banned Half-Life 2 mod Missing Information. Valve eventually allowed players to download and play Missing Information, and the mod recently went through the Steam Greenlight program—and was approved.


Another reason the leak continues to fascinate is the absence of any concrete information about Half-Life 3, Half-Life 2: Episode Three or whatever Valve might call the long-rumored continuation of Gordon Freeman’s journey. Until that happens, I suspect players will continue to mine this for whatever they can.

You can reach the author of this post at or on Twitter at @patrickklepek.


That Actually Happened is a weekly series at Kotaku in which we highlight interesting moments in gaming history. So far, we’ve revisited when Sonic kissed a human, a live game show on Xbox 360, and Sony throwing a God of War party with a dead goat. If you have any suggestions for future entires, please let us know in the comments.