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Win32/Captiya


Win32/Captiya is a trojan that tries to decode CAPTCHA. CAPTCHA is an acronym for 'Completely Automated Public Turing test to tell Computers and Humans Apart', which is usually used for creating new e-mail accounts. Decoded CAPTCHAs can be used to automatically register e-mail accounts. The automatic mass creation of e-mail accounts can be used for spamming or other malicious activities.
Win32/Captiya works in concert with Spammer:Win32/Newacc.A in order to automatically registers new e-mail accounts, and communicates with a Web Service in order to bypass CAPTCHA protection. Win32/Captiya communicates to remote sites in order to aid and complete the registration of new accounts.


What to do now

To detect and remove this threat and other malicious software that may be installed on your computer, run a full-system scan with an appropriate, up-to-date, security solution. The following Microsoft products will detect and remove this threat:
 
 
For more information on antivirus software, see http://www.microsoft.com/windows/antivirus-partners/.

Threat behavior

Win32/Captiya is a trojan that tries to decode CAPTCHA. CAPTCHA is an acronym for 'Completely Automated Public Turing test to tell Computers and Humans Apart', which is usually used for creating new e-mail accounts. Decoded CAPTCHAs can be used to automatically register e-mail accounts. The automatic mass creation of e-mail accounts can be used for spamming or other malicious activities.
Installation
Win32/Captiya has been observed in the wild being distributed with some variants of Spammer:Win32/Newacc.A. This is an attacker tool that automatically registers new e-mail accounts on Hotmail, AOL, Gmail, Lycos and other account service providers.
 
Payload
Decodes CAPTCHAs
This trojan tries to decode captcha by comparing characters in the image to different fonts. Among the fonts used are the following:
 
Aldine32
Arial
Courier
Decker
Helevetica
Additional Information
The trojan may be used in conjunction with other malware that can automatically create new e-mail accounts (such as Spammer:Win32/Newacc.A) - the newly created accounts can then be used for spamming or other nefarious activities.
 
Analysis by Elda Dimakiling

Symptoms

System Changes
The following system changes may indicate the presence of Win32/Captiya:
  • Presence of one of the following file names in the %windir% folder:
    mm_tmpoc1.exe
    mmoc1.exe
    mm_tmpoc2.exe
    mmoc2.exe

Prevention

Take the following steps to help prevent infection on your computer:
  • Enable a firewall on your computer.
  • Get the latest computer updates for all your installed software.
  • Use up-to-date antivirus software.
  • Limit user privileges on the computer.
  • Use caution when opening attachments and accepting file transfers.
  • Use caution when clicking on links to webpages.
  • Avoid downloading pirated software.
  • Protect yourself against social engineering attacks.
  • Use strong passwords.
Enable a firewall on your computer
Use a third-party firewall product or turn on the Microsoft Windows Internet Connection Firewall.
Get the latest computer updates
Updates help protect your computer from viruses, worms, and other threats as they are discovered. It is important to install updates for all the software that is installed in your computer. These are usually available from vendor websites.
 
You can use the Automatic Updates feature in Windows to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
Use up-to-date antivirus software
Most antivirus software can detect and prevent infection by known malicious software. To help protect you from infection, you should always run antivirus software, such as Microsoft Security Essentials, that is updated with the latest signature files. For more information, see http://www.microsoft.com/windows/antivirus-partners/.
Limit user privileges on the computer
Starting with Windows Vista and Windows 7, Microsoft introduced User Account Control (UAC), which, when enabled, allowed users to run with least user privileges. This scenario limits the possibility of attacks by malware and other threats that require administrative privileges to run.
 
You can configure UAC in your computer to meet your preferences:
Use caution when opening attachments and accepting file transfers
Exercise caution with email and attachments received from unknown sources, or received unexpectedly from known sources. Use extreme caution when accepting file transfers from known or unknown sources.
Use caution when clicking on links to webpages
Exercise caution with links to webpages that you receive from unknown sources, especially if the links are to a webpage that you are not familiar with, unsure of the destination of, or suspicious of. Malicious software may be installed in your computer simply by visiting a webpage with harmful content.
Avoid downloading pirated software
Threats may also be bundled with software and files that are available for download on various torrent sites. Downloading "cracked" or "pirated" software from these sites carries not only the risk of being infected with malware, but is also illegal. For more information, see 'The risks of obtaining and using pirated software'.
Protect yourself from social engineering attacks
While attackers may attempt to exploit vulnerabilities in hardware or software to compromise a computer, they also attempt to exploit vulnerabilities in human behavior to do the same. When an attacker attempts to take advantage of human behavior to persuade the affected user to perform an action of the attacker's choice, it is known as 'social engineering'. Essentially, social engineering is an attack against the human interface of the targeted computer. For more information, see 'What is social engineering?'.
Use strong passwords
Attackers may try to gain access to your Windows account by guessing your password. It is therefore important that you use a strong password – one that cannot be easily guessed by an attacker. A strong password is one that has at least eight characters, and combines letters, numbers, and symbols. For more information, see http://www.microsoft.com/protect/yourself/password/create.mspx.

Alert level: Severe
This entry was first published on: Apr 29, 2008
This entry was updated on: Apr 17, 2011

This threat is also detected as:
No known aliases