one good question is - ' Is it possible for us to find out the trojan. Because we normally double click on any attachment before that we should have the knowledge about that file so that we will not open it?'


well for that
One thing to watch for is that the file is not an .exe file. Look at the name of the attachment. Does it say something.exe. If that is the case then don't click that attachment. I'm sure they can be named in different ways where you can't tell. If you plan on opening one of these files, see if you can scan it first. There are sooooooo many ways of doing it though, it's hard to keep up with.

also


'Trojan' Stop is used to scan and remove trojan horses, viruses, and spyware from your PC, and protect your PC.

You can remove trojan horses, viruses, and spyware from your PC and prevent unwanted software from being installed without your knowledge.

more ways can be
GFI MailSecurity for Exchange/SMTP is an email content checking, exploit detection, Trojan and executable scanning, threats analysis and anti-virus solution that removes all types of email-borne threats before they can affect your email users. GFI MailSecurity's key features include multiple virus engines, for virus engine independence and better security; email content and attachment checking, to quarantine dangerous attachments and content; an exploit shield, to detect emails with OS and application exploits; an HTML threats engine, to disable HTML scripts; and a Trojan & Executable Scanner, to detect potentially malicious executables. Read more and download a trial version by clicking here.

GFI DownloadSecurity for ISA Server which enables you to assert control over what files your users download from HTTP and FTP sites. Downloaded files are content checked for malicious content, viruses, and Trojans and can be quarantined based on file type and user. GFI DownloadSecurity handles the security risk of file downloads without resorting to blocking all file downloads at firewall leve


at last TRY
http://www.awprofessional.com/content/images/0321356411/samplechapter/Conry_ch05.pdf