This type of trojan secretly downloads malicious files from a remote server, then installs and executes the files.
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Trojan-Downloader:W32/Small.COY belongs to a family of known primitive trojan downloaders that have a download URL encrypted in the end of their files. The URL to this particular trojan downloader (smsender.exe file) was spammed in e-mails to a large number of addresses.
When downloaded and run by a recipient, the trojan-downloader attempts to download and activate a file named installer2.0.26.exe from a website hosted in Canada.
The downloaded file is detected as 'Trojan-PSW.Win32.Agent.fy' and it is technically a trojan dropper. Once activated, it drops a DLL file and registers it as a component of Internet Explorer. This DLL file is the main spying component and it is activated when Internet Explorer is run. The spying component collects and sends out the following data:
- Data from webforms that a user fills in including the URLs of the site
- POP and SMTP (e-mail) account login names and passwords
- HTTP e-mail account login names and passwords
- MSN passwords
- Outlook account information
- Internet Explorer passwords for protected sites
- IE autocomplete fields data
- Information about an infected computer
- Windows cached passwords
The trojan can also create a batch file that deletes system files from the Program Files and System Root (main Windows directory) folders.