1 Measurement and Classification of Humans and Bots in Internet Chat By Steven Gianvecchio, Mengjun Xie, Zhenyu Wu, and Haining Wang College of William and Mary

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 2 Outline  Background  Measurement  Classification System  Experimental Evaluation  Conclusion

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 3 Outline  Background  Measurement  Classification System  Experimental Evaluation  Conclusion

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 4 Bots  Bots - programs that automate human tasks  web bots automate browsing the web  chat bots automate online chat  can be harmful and/or helpful

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 5 Chat Bots vs. BotNets  BotNets – networks of compromised machines  some use chat systems (IRC) for C&C, others use P2P, HTTP, etc.  abuse various systems  Chat Bots – automated chat programs  some are helpful, e.g., chat loggers  can abuse chat systems and their users

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 6 The Chat Bot Problem MSN  The Problem – chat bots abuse chat services (e.g., AOL, Yahoo!, MSN)  send spam  spread malicious software  mount phishing attacks  Our focus is on the Yahoo! chat system

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 7 A Typical Chat Alice12 entered the room. Alice12: Hi room. Alice12 entered the room. Alice12: Hi room. Bob34: hi alice Alice12 entered the room. Alice12: Hi room. Bob34: hi alice Susie88: any guys want to let a cute girl move in with them! hehe Alice12 entered the room. Alice12: Hi room. Bob34: hi alice Susie88: any guys want to let a cute girl move in with them! hehe Alice12: What’s up? Alice12 entered the room. Alice12: Hi room. Bob34: hi alice Susie88: any guys want to let a cute girl move in with them! hehe Alice12: What’s up? Bob34: not much Alice12 entered the room. Alice12: Hi room. Bob34: hi alice Susie88: any guys want to let a cute girl move in with them! hehe Alice12: What’s up? Bob34: not much Susie88: can you guys see me on my web-cam?? (its in my profile)

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 8 Yahoo! Chat  Yahoo! chat is a large commercial chat service  over 3,000 chat rooms AUTH, CHAT, IM, …

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 9 Yahoo! Chat  Yahoo! chat system  client connects to a server  servers relay messages to/from clients

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 10 Outline  Background  Measurement  Classification System  Experimental Evaluation  Conclusion

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 11 Measurement  August-November 2007 – we collect data  August 2007 – Yahoo! adds CAPTCHA  must pass to join a chat room  protocol update, prevents some 3 rd party clients from accessing chat  October 2007 – bots are back  some bots return before 3 rd party clients

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 12 Measurement  September and October 2007  very few chat bots  August and November 2007  many chat bots  1,440 hours of chat logs  147 chat logs  21 chat rooms

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 13 Measurement  To create our dataset, we read and label the chat users as  human, bot, or ambiguous  In total, we recognized 14 different types of chat bots  different triggering mechanisms  different text generation techniques

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 14 Triggering Mechanisms  Timer-Based  periodic timers, e.g., 40 seconds  random timers, e.g., seconds  Response-Based  responds to other users Sam77: Bob12, you’re just full of questions, aren’t you? Sam77: Bob12, lots of evidence for evolution can be found here

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 15 Text Generation  Character Padding Fiona88: anyone boredjn wanna chat?uklcss  Synonym Phrases Marjorie99: Hi Babes! Marjorie Here! Inspect My Site Marjorie99: Mmmm Folks! Im Marjorie! View My Webpage  Odd Line or Word Spacing  Message Replay

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 16 Types of Chat Bots  Periodic Bots – sends messages based on periodic timers  Random Bots – sends messages based on random timers  Responder Bots – responds to messages of other users  Replay Bots – replays messages of other users

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 17  Humans  inter-message delay – evidence of heavy tail  message size – well fit by Exponential (λ=0.034)

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 18  Periodic Bots  inter-message delay – several clusters with high probabilities  message size – messages built from templates approximate a normal distribution

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 19  Random Bots  inter-message delay – Equilikely distribution at 40, 64, and 88; Uniform distribution  message size – messages selected from a small database

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 20  Responder Bots  inter-message delay – human-like timing  message size – multiple templates of different lengths

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 21  Replay Bots  inter-message delay – cluster with high probabilities (replay bots are periodic)  message size – human-like size, well fit by Exponential (λ=0.028)

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 22 Outline  Background  Measurement  Classification System  Experimental Evaluation  Conclusion

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 23 Classification System  Entropy Classifier  detects abnormal behavior  based on message sizes and inter-message delays  accurate but slow  Machine Learning Classifier  detects “learned” patterns  based on message content  fast but must be trained

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 24  Observation – chat bots are less complex than humans, and thus, lower in entropy  exploits the low entropy of chat bots  Corrected Conditional Entropy Test (CCE)  estimates higher-order entropy  Entropy Test (EN)  estimates first-order entropy Entropy Classifier

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 25 Machine Learning Classifier  Observation - chat spam like spam is a text classification problem  exploits message content of chat bots  CRM114  a powerful text classification system  several built-in classifiers: HMM, KNN/Hyperspace, OSB, SVM, Winnow, etc.  we use OSB

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 26  Hybrid Classification System  entropy classifier builds and maintains the bot corpus  machine learning classifier uses the bot and human corpora BOT CORPUS CLASSIFY AS CHAT BOT HUMAN CORPUS CLASSIFY AS HUMAN INPUT ENTROPY CLASSIFIER MACHINE LEARNING CLASSIFIER

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 27 Outline  Background  Measurement  Classification System  Experimental Evaluation  Conclusion

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 28 Experimental Evaluation  Types of Chat Bots  Periodic Bots  Random Bots  Responder Bots  Replay Bots  Classifiers  entropy classifier – 100 messages  machine learning classifier – 25 messages

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 29 Experimental Evaluation  Classification Tests  Ent – entropy classifier  SupML – fully-supervised ML classifier, trained on AUG BOTS  SupMLre – fully-supervised ML classifier, retrained on NOV BOTS  EntML – entropy-trained ML

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 30 AUG BOTSNOV BOTS periodicrandomrespondperiodicrandomreplayhuman test TP FP EN(imd) 121/12168/681/3051/51109/10940/407/1713 CCE(imd) 121/12149/684/3051/51109/10940/4011/1713 EN(ms) 92/1217/688/3046/5134/1090/407/1713 CCE(ms) 77/1218/6830/3051/516/1090/4011/1713 OVERALL 121/12168/6830/3051/51109/10940/4017/1713  Entropy Classifier  EN – entropy  CCE – corrected conditional entropy  (imd) – inter-message delay  (ms) – message size

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 31 AUG BOTSNOV BOTS periodicrandomrespondperiodicrandomreplayhuman test TP FP EN(imd) 121/12168/681/3051/51109/10940/407/1713 CCE(imd) 121/12149/684/3051/51109/10940/4011/1713 EN(ms) 92/1217/688/3046/5134/1090/407/1713 CCE(ms) 77/1218/6830/3051/516/1090/4011/1713 OVERALL 121/12168/6830/3051/51109/10940/4017/1713  EN(imd) and CCE(imd)  problems against responder bots  detect most other chat bots

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 32 AUG BOTSNOV BOTS periodicrandomrespondperiodicrandomreplayhuman test TP FP EN(imd) 121/12168/681/3051/51109/10940/407/1713 CCE(imd) 121/12149/684/3051/51109/10940/4011/1713 EN(ms) 92/1217/688/3046/5134/1090/407/1713 CCE(ms) 77/1218/6830/3051/516/1090/4011/1713 OVERALL 121/12168/6830/3051/51109/10940/4017/1713  EN(ms) and CCE(ms)  problems against random and replay bots  detect most other chat bots

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 33 AUG BOTSNOV BOTS periodicrandomrespondperiodicrandomreplayhuman test TP FP EN(imd) 121/12168/681/3051/51109/10940/407/1713 CCE(imd) 121/12149/684/3051/51109/10940/4011/1713 EN(ms) 92/1217/688/3046/5134/1090/407/1713 CCE(ms) 77/1218/6830/3051/516/1090/4011/1713 OVERALL 121/12168/6830/3051/51109/10940/4017/1713  OVERALL  detects all chat bots  false positive rate is ~0.01  100 messages

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 34 AUG BOTSNOV BOTS periodicrandomrespondperiodicrandomreplayhuman test TP FP Ent 121/12168/6830/3051/51109/10940/4017/1713 SupML 121/12168/6830/3014/51104/1091/400/1713 SupMLre 121/12168/6830/3051/51109/10940/400/1713 EntML 121/12168/6830/3051/51109/10940/401/1713  Entropy and Machine Learning Classifiers  Ent – entropy classifier (from last slide)  SupML – fully-supervised machine learning  SupMLre – SupML retrained  EntML – entropy-trained machine learning

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 35 AUG BOTSNOV BOTS periodicrandomrespondperiodicrandomreplayhuman Test TP FP Ent 121/12168/6830/3051/51109/10940/4017/1713 SupML 121/12168/6830/3014/51104/1091/400/1713 SupMLre 121/12168/6830/3051/51109/10940/400/1713 EntML 121/12168/6830/3051/51109/10940/401/1713  Ent  OVERALL results from previous slide

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 36 AUG BOTSNOV BOTS periodicrandomrespondperiodicrandomreplayhuman test TP FP Ent 121/12168/6830/3051/51109/10940/4017/1713 SupML 121/12168/6830/3014/51104/1091/400/1713 SupMLre 121/12168/6830/3051/51109/10940/400/1713 EntML 121/12168/6830/3051/51109/10940/401/1713  SupML  has problems against November bots  needs to be retrained for new bots  SupMLre  detects all bots

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 37 AUG BOTSNOV BOTS periodicrandomrespondperiodicrandomreplayhuman test TP FP Ent 121/12168/6830/3051/51109/10940/4017/1713 SupML 121/12168/6830/3014/51104/1091/400/1713 SupMLre 121/12168/6830/3051/51109/10940/400/1713 EntML 121/12168/6830/3051/51109/10940/401/1713  EntML  false positive rate is ~ (Ent is ~0.01)  25 messages

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 38 Outline  Background  Measurement  Classification System  Experimental Evaluation  Conclusion

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 39 Conclusion  Measurements  overall, chat bots are less complex than humans  some chat bots more human-like  Classification System  exploits benefits of both classifiers  quickly classifies known chat bots  accurately classifies unknown chat bots

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 40 Conclusion (cont.)  Future Work  investigate more advanced chat bots  explore applications of entropy on other forms of bots (e.g., web bots)  explore other applications of entropy (e.g., detecting covert timing channels)

USENIX Security 2008 Measurement and Classification of Humans and Bots in Internet Chat 41 Questions? Thank You!