Justin   California, United States
Reverse engineering hobbyist, TF2 bug-investigator, bug-reporter, bug-fixer, modder, etc. I have a backlog of friend requests and it's hard to keep track of people, so leave a comment if you really need me to add you.

I run Arch Linux on my desktop computer, but I run games in Windows on a custom virtual machine (KVM with some modifications) that allows my second graphics card (as well as my mouse and keyboard) to be directly accessed with minimal performance impact. So instead of dual booting, I run Linux and Windows simultaneously with full graphics acceleration in each.
Currently Offline
Last Online 3 days ago
Who is this guy?
Am I the same person as user sigsegv_banana on HackerOne? No.

I like to analyze TF2 (the MvM gamemode in particular) and figure out exactly how the various parts of the game work. I post walls of text explaining how things work or why things are broken on the SCUD MvM forums; I make videos demonstrating stuff and post them to YouTube; I run tests and create detailed graphs; I figure out things that are buggy in the game, and track down why they don't work; I make mods to fix and tweak various things; and I report bugs to Valve so they can fix them. Sometimes, I find time to actually play the game.

These days, I spend most of my time looking through the TF2 game code (via disassembly, not the actual current source code) to figure out how various aspects of the game work, especially the bot AI. I debug problems and try to come up with creative ways to fix them. I do my best to tell custom MvM mission creators about the types of things that are possible that they may not know about.

I've learned a lot along the way.

Discord ID: sigsegv#5577

FAQ: What were your Finder's Fee hats and community weapons for?
The community weapons were a thank-you from the TF Team for submitting lots of detailed gameplay related bug reports. I estimate I've sent them in excess of 100 emails cumulatively with bug reports over the past two years or so.

The first Finder's Fee was for reporting a potential arbitrary code execution exploit in Source engine. The second Finder's Fee was for reporting another arbitrary code execution exploit specifically in Team Fortress 2 (for this one I worked together with PistonMiner and we crafted a working proof-of-concept exploit file that could successfully execute code of our choosing). The third Finder's Fee was for reporting yet another arbitrary code execution exploit in Team Fortress 2 (another collaboration with PistonMiner).

FAQ: You're hard to reach. How the hell can I get in contact with you?
People are constantly sending me Steam invites and leaving comments and messages on YouTube and Reddit asking me to look into things, and it's impossible to keep track of everyone who's asked me questions or requested that I look into something. I just don't have the time to respond to everything, so lots of stuff ends up slipping through the cracks.

Some reliable ways to contact me (for example, if you have something really important to tell me and I haven't gotten around to your friend request, or something):
1. Send a Reddit message to /u/sigsegv__
2. Send a YouTube message via my sigsegv channel
3. Send an email to sigsegv at

I am usually "offline" on Steam, but you can still send me a Steam message and there's a very high chance I will see it.

My MvM server
In mid-2015, I was really annoyed at the increasing number of bugs in Mann vs Machine mode, so I took it upon myself to set up a dedicated server with a bunch of small server mods to fix various bugs, improve some of the more annoying aspects of the game mode, and generally make an MvM experience that's better than what you'll get on a Valve Mann Up server.

Website: [] info for connecting and a detailed (but preposterously outdated) list of the installed server mods
Forum thread: posts about updates to mods, discussion about custom missions, etc.

Steam URL for direct connection: steam://connect/

1. YouTube: I post TF2 (primarily MvM) analysis videos frequently. Mostly brief, sometimes in-depth.
2. GitHub: [] you can look at the source code for my server mods and other related things.
3. GameBanana: [] I've made a few client-side improvement mods for MvM.

My medical situation
I used to have some information here, but I've gotten tired of people constantly repeating factually incorrect things about my health situation and personal life. So, kindly knock it off and let me speak for myself on those matters. Thanks.
Favorite Guide
Created by - sigsegv
525 ratings
TFBots can have one of four different difficulty/skill levels: Easy, Normal, Hard, and Expert. It's obvious that Expert bots are much better than Easy bots, but what are the exact differences between each of the skill levels? Valve has never fully document

Recent Activity

8,348 hrs on record
last played on Aug 20
129 hrs on record
last played on Aug 20
40 hrs on record
last played on Aug 19
Professor Heavy Aug 19 @ 3:48pm 
CC is not an official update.
felix Aug 19 @ 1:23pm 
CC is a official update?
TheYammi Aug 18 @ 4:06pm 
Hi, Sigsegv, I know of a Sticky Bomb exploit. It isn't quite game breaking, but can easily be abused by any player. It involves a demoman placing 3 or more sticky bombs in the same place. I can give you more information.
ʙsi | egn Aug 5 @ 1:04pm 
Hey sig, I've found a NOT-game-breaking bug in TF2 that involves the Crusader's Crossbow and not being able to fire with it. I can give you the details.
AFKSpy Aug 5 @ 1:48am 
Hi, I'm trying to get a bunch of old demos (pre-goldrush) to load in an up-to-date version of tf2. For that I would like to know how strings are encoded in bf_write buffers. I need that to edit SVC_ServerInfo in the .dem file. I really appreciate your contributions to tf2 and hope your deep knowledge of the source code might help me out :)
Stockholm Aug 1 @ 4:56pm 
Hello, I'm adding you to ask a few questions related to TF2.