Man-in-the-browser (MITB, MitB, MIB, MiB), a form of Internet threat related to man-in-the-middle (MITM), is a proxy Trojan horse[1] that infects a web browser by taking advantage of vulnerabilities in browser security to modify web pages, modify transaction content or insert additional transactions, all in a completely covert fashion invisible to both the user and host web application. A MitB attack will be successful irrespective of whether security mechanisms such as SSL/PKI and/or two or three-factor Authentication solutions are in place. A MitB attack may be countered by using out-of-band transaction verification, although SMS verification can be defeated by man-in-the-mobile (MitMo) malware infection on the mobile phone. Trojans may be detected and removed by antivirus software[2] with a 23% success rate against Zeus in 2009,[3] and still low rates in 2011.[4] The 2011 report concluded that additional measures on top of antivirus were needed.[4] A related, simpler attack is the boy-in-the-browser (BitB, BITB). The majority of financial service professionals in a survey considered MitB to be the greatest threat to online banking and Microsoft Outlook.


The MitB threat was demonstrated by Augusto Paes de Barros in his 2005 presentation about backdoor trends "The future of backdoors - worst of all worlds".[5] The name "Man-in-the-Browser" was coined by Philipp Gühring on 27 January 2007.[6]

A MitB Trojan works by using common facilities provided to enhance browser capabilities such as Browser Helper Objects (a feature limited to Internet Explorer), browser extensions and user scripts (for example in JavaScript) etc.[6] Antivirus software can detect some of these methods.[2]

In a nutshell example exchange between user and host, such as an Internet banking funds transfer, the customer will always be shown, via confirmation screens, the exact payment information as keyed into the browser. The bank, however, will receive a transaction with materially altered instructions, i.e. a different destination account number and possibly amount. The use of strong authentication tools simply creates an increased level of misplaced confidence on the part of both customer and bank that the transaction is secure. Authentication, by definition, is concerned with the validation of identity credentials. This should not be confused with transaction verification.


Examples of MitB threats on different operating systems and web browsers:

Man-in-the-Browser examples
NameDetailsOperating systemBrowser
Agent.DBJP[7]WindowsIE, Firefox
Bugat[8]WindowsIE, Firefox
Carberptargets Facebook users redeeming e-cash vouchers[9]WindowsIE, Firefox
ChromeInject*[10]Greasemonkey impersonator[11]WindowsFirefox
Gozi[1]WindowsIE, Firefox
OddJob[13]keeps bank session openWindowsIE, Firefox
Silentbanker[14]WindowsIE, Firefox
SpyEye[16]successor of Zeus, widespread, low detectionWindowsIE, Firefox
Sunspot[17]widespread, low detectionWindowsIE, Firefox
Tatanga[18]WindowsIE, Firefox, Chrome, Opera, Safari, Maxthon, Netscape, Konqueror
Tiny Banker Trojan[19]Smallest banking Trojan detected in wild at 20KBWindowsIE, Firefox
Torpig**[15]WindowsIE, Firefox
URLZone****[1]WindowsIE, Firefox, Opera
Weyland-Yutani BOT[20]crimeware kit similar to Zeus, not widespread[20][21]Mac OS XFirefox
Zeus***[12]widespread, low detectionWindowsIE, Firefox
KeyWindows: IEWindows: IE & Firefox or FirefoxWindows: otherMac OS X: any
*ChromeInject a.k.a. ChromeInject.A, ChromeInject.B, Banker.IVX, Inject.NBT, Bancos-BEX, Drop.Small.abw[10]
**Torpig a.k.a. Sinowal, Anserin[1]
***Zeus a.k.a. ZeuS, Zbot,[22] Wsnpoem,[23][24] NTOS,[3] PRG,[3] Kneber,[25] Gorhax[25]
****URLZone a.k.a. Bebloh!IK, Runner.82176, Monder, ANBR, Sipay.IU, Runner.fq, PWS.y!cy, Zbot.gen20, Runner.J, BredoPk-B, Runner.EQ



Known Trojans may be detected, blocked and removed by antivirus software.[2] In a 2009 study, the effectiveness of antivirus against Zeus was 23%,[3] and again low success rates were reported in a separate test in 2011.[4] The 2011 report concluded that additional measures on top of antivirus were needed.[4]

Hardened software

  • Browser security software: MitB attacks may be blocked by in-browser security software such as Trusteer Rapport for Microsoft Windows and Mac OS X which blocks the APIs from browser extensions and controls communication.[11][12][15]
  • Alternative software: Reducing or eliminating the risk of malware infection by using portable applications or using alternatives to Microsoft Windows like Mac OS X, Linux, or mobile OSes Android, iOS, Chrome OS, Windows Mobile, Symbian etc., and/or browsers Chrome, Opera.[26] Further protection can be achieved by running this alternative OS, like Linux, from a non-installed live CD, or Live USB.[27]
  • Secure Web Browser: Several vendors can now provide a two-factor security solution where a Secure Web Browser is part of the solution. In this case MitB attacks are avoided as the user executes a hardened browser from their two-factor security device rather than executing the "infected" browser from their own machine.

Out-of-band transaction verification

A theoretically effective method of combating any MitB attack is through an out-of-band (OOB) transaction verification process. This overcomes the MitB trojan by verifying the transaction details, as received by the host (bank), to the user (customer) over a channel other than the browser; for example an automated telephone call, SMS, or a dedicated mobile app with graphical cryptogram.[28] OOB transaction verification is ideal for mass market use since it leverages devices already in the public domain (e.g. landline, mobile phone, etc.) and requires no additional hardware devices yet enables three-factor authentication (using voice biometrics), transaction signing (to non-repudiation level) and transaction verification. The downside is that the OOB transaction verification adds to the level of the end-user's frustration with more and slower steps.


Mobile phone mobile Trojan spyware man-in-the-mobile (MitMo)[29] can defeat OOB SMS transaction verification.[30]

  • ZitMo (Zeus-In-The-Mobile) is not a MitB Trojan itself (although it performs a similar proxy function on the incoming SMSes), but is mobile malware suggested for installation on a mobile phone by a Zeus infected computer. By intercepting all incoming SMSes, it defeats SMS-based banking OOB two-factor authentication on Windows Mobile, Android, Symbian, BlackBerry.[30] ZitMo may be detected by Antivirus running on the mobile device.
  • SpitMo (SpyEye-In-The-Mobile, SPITMO), is similar to ZitMo.[31]

Web fraud detection

Web Fraud Detection can be implemented at the bank to automatically check for anomalous behaviour patterns in transactions.[32]

Proxy trojans

Keyloggers are the most primitive form of proxy trojans, followed by browser-session recorders which capture more data, and lastly MitBs are the most sophisticated type.[1]


SSL/PKI etc. may offer protection in a man-in-the-middle attack, but offers no protection in a man-in-the-browser attack.


A related attack that is simpler and quicker for malware authors to set up is termed boy-in-the-browser (BitB or BITB). Malware is used to change the client's computer network routing to perform a classic man-in-the-middle attack. Once the routing has been changed, the malware may completely remove itself, making detection more difficult.[33]


Clickjacking tricks a web browser user into clicking on something different from what the user perceives, by means of malicious code in the webpage.

See also


  1. 1 2 3 4 5 Bar-Yosef, Noa (2010-12-30). "The Evolution of Proxy Trojans". Retrieved 2012-02-03.
  2. 1 2 3 4 F-Secure (2007-02-11). "Threat Description: Trojan-Spy:W32/Nuklus.A". Retrieved 2012-02-03.
  3. 1 2 3 4 Trusteer (2009-09-14). "Measuring the in-the-wild effectiveness of Antivirus against Zeus" (PDF). Archived from the original (PDF) on November 6, 2011. Retrieved 2012-02-05.
  4. 1 2 3 4 Quarri Technologies, Inc (2011). "Web Browsers: Your Weak Link in Achieving PCI Compliance" (PDF). Retrieved 2012-02-05.
  5. Paes de Barros, Augusto (15 September 2005). "O futuro dos backdoors - o pior dos mundos" (PDF) (in Portuguese). Sao Paulo, Brazil: Congresso Nacional de Auditoria de Sistemas, Segurança da Informação e Governança - CNASI. Archived from the original (PDF) on July 6, 2011. Retrieved 2009-06-12.
  6. 1 2 Gühring, Philipp (27 January 2007). "Concepts against Man-in-the-Browser Attacks" (PDF). Retrieved 2008-07-30.
  7. Dunn, John E (2010-07-03). "Trojan Writers Target UK Banks With Botnets". Retrieved 2012-02-08.
  8. Dunn, John E (2010-10-12). "Zeus not the only bank Trojan threat, users warned". Retrieved 2012-02-03.
  9. Curtis, Sophie (2012-01-18). "Facebook users targeted in Carberp man-in-the-browser attack". Retrieved 2012-02-03.
  10. 1 2 Marusceac Claudiu Florin (2008-11-28). "Trojan.PWS.ChromeInject.B Removal Tool". Retrieved 2012-02-05.
  11. 1 2 3 Nattakant Utakrit, School of Computer and Security Science, Edith Cowan University (2011-02-25). "Review of Browser Extensions, a Man-in-theBrowser Phishing Techniques Targeting Bank Customers". Retrieved 2012-02-03.
  12. 1 2 3 Symantec Marc Fossi (2010-12-08). "ZeuS-style banking Trojans seen as greatest threat to online banking: Survey". Retrieved 2012-02-03.
  13. Ted Samson (2011-02-22). "Crafty OddJob malware leaves online bank accounts open to plunder". Retrieved 2012-02-06.
  14. Symantec Marc Fossi (2008-01-23). "Banking with Confidence". Retrieved 2008-07-30.
  15. 1 2 3 4 Trusteer. "Trusteer Rapport". Retrieved 2012-02-03.
  16. CEO of Trusteer Mickey Boodaei (2011-03-31). "Man-in-the-Browser attacks target the enterprise". Retrieved 2012-02-03.
  17. (2011-05-11). "Explosive financial malware targets Windows". Retrieved 2012-02-06.
  18. Jozsef Gegeny; Jose Miguel Esparza (2011-02-25). "Tatanga: a new banking trojan with MitB functions". Retrieved 2012-02-03.
  19. "Tiny 'Tinba' Banking Trojan Is Big Trouble". Retrieved 2016-02-28.
  20. 1 2 Borean, Wayne (2011-05-24). "The Mac OS X Virus That Wasn't". Retrieved 2012-02-08.
  21. Fisher, Dennis (2011-05-02). "Crimeware Kit Emerges for Mac OS X". Archived from the original on September 5, 2011. Retrieved 2012-02-03.
  22. F-secure. "Threat DescriptionTrojan-Spy:W32/Zbot". Retrieved 2012-02-05.
  23. Hyun Choi; Sean Kiernan (2008-07-24). "Trojan.Wsnpoem Technical Details". Symantec. Retrieved 2012-02-05.
  24. Microsoft (2010-04-30). "Encyclopedia entry: Win32/Zbot - Learn more about malware - Microsoft Malware Protection Center". Symantec. Retrieved 2012-02-05.
  25. 1 2 Richard S. Westmoreland (2010-10-20). "Antisource - ZeuS". Archived from the original on 2012-01-20. Retrieved 2012-02-05.
  26. Horowitz, Michael (2012-02-06). "Online banking: what the BBC missed and a safety suggestion". Retrieved 2012-02-08.
  27. Purdy, Kevin (2009-10-14). "Use a Linux Live CD/USB for Online Banking". Retrieved 2012-02-04.
  28. Finextra Research (2008-11-13). "Commerzbank to deploy Cronto mobile phone-based authentication technology". Retrieved 2012-02-08.
  29. Chickowski, Ericka (2010-10-05). "'Man In The Mobile' Attacks Highlight Weaknesses In Out-Of-Band Authentication". Retrieved 2012-02-09.
  30. 1 2 Schwartz, Mathew J. (2011-07-13). "Zeus Banking Trojan Hits Android Phones". Retrieved 2012-02-04.
  31. Balan, Mahesh (2009-10-14). "Internet Banking & Mobile Banking users beware – ZITMO & SPITMO is here !!". Retrieved 2012-02-05.
  32. Sartain, Julie (2012-02-07). "How to protect online transactions with multi-factor authentication". Retrieved 2012-02-08.
  33. Imperva (2010-02-14). "Threat Advisory Boy in the Browser". Retrieved 2015-03-12.
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