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'''PGPCoder''', also known as '''GPCode''', is a [[trojan horse (computing)|trojan]] that encrypts files on the infected computer and then asks for a fee in order to release these files. This is a new type of behavior, rarely seen until now, dubbed [[ransomware (malware)|ransomware]] or [[cryptovirology]].
== Trojan ==
Once installed on a computer, the trojan creates two registry keys: one to ensure it is run on every system startup, and the second to monitor the progress of the trojan in the infected computer, counting the number of files that have been analyzed by the malicious code.
Once it has been run, the trojan embarks on its mission, which is to encrypt, using a digital encryption key, all the files it finds on computer drives with extensions corresponding to those listed in its code. These extensions include
The blackmail is completed with the trojan dropping a text file in each directory, with instructions to the victim of what to do. An email address is supplied through which users are supposed to request for their files to be released after paying a ransom of $100-200 to an [[e-gold]] or [[Liberty Reserve]] account.<ref>{{cite web|url=http://rump2008.cr.yp.to/6b53f0dad2c752ac2fd7cb80e8714a90.pdf|title=Cryptanalysis of the Gpcode.ak ransomware virus|author=Eran Tromer|acccessdate=2008-09-30}}</ref>▼
▲The blackmail is completed with the trojan dropping a text file in each directory, with instructions to the victim of what to do. An email address is supplied through which users are supposed to request for their files to be released after paying a ransom of $200.
== Efforts to combat the trojan ==
While a few Gpcode variants have been successfully implemented<ref>{{cite web|url=http://www.kaspersky.com/news?id=207575651|title=Kaspersky Lab announces the launch of Stop Gpcode, an international initiative against the blackmailer virus|date=2008-06-09}}</ref>, many variants have flaws that allow users to recover data without paying the ransom fee. The first versions of Gpcode used a custom-written encryption routine that was easily broken.<ref>{{cite web|url=http://www.viruslist.com/en/analysis?pubid=189678219|title=Blackmailer: the story of Gpcode|date=2006-07-26|publisher=Kaspersky Labs}}</ref> Variant Gpcode.ak writes the encrypted file to a new ___location, and deletes the unencrypted file, and this allows an [[undeletion|undeletion utility]] to recover some of the files. Once some encrypted+unencrypted pairs have been found, this sometimes gives enough information to decrypt other files.<ref>{{cite web|url=http://support.kaspersky.com/faq/?qid=208279822|title=Utilities which fight Virus.Win32.Gpcode.ak|date=2008-06-25|publisher=Kaspersky Lab}}</ref><ref>{{cite web|url=http://www.viruslist.com/en/weblog?weblogid=208187531|title=Restoring files attacked by Gpcode.ak|publisher=Kaspersky Labs|date=2008-06-13}}</ref><ref>{{cite web|url=http://www.viruslist.com/en/weblog?weblogid=208187538|title=Another way of restoring files after a Gpcode attack|date=2008-06-26}}</ref> Variant Gpcode.am uses symmetric encryption, which made decryption very easy.<ref>{{cite web|url=http://www.viruslist.com/en/weblog?weblogid=208187565|title=New Gpcode - mostly hot air|date=2008-08-14|publisher=Kaspersky Labs}}</ref>
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