MS-DOS

cricri is a virus that spreads to other computers by copying its code to other files or programs.

cricri uses the following propagation or distribution methods:

• Exploiting vulnerabilities with the intervention of the user: exploiting vulnerabilities in file formats or applications. To exploit them successfully it needs the intervention of the user: opening files, viewing malicious web pages, reading emails, etc.
• File infection: it infects different types of files, which are then distributed through any of the usual means: floppy disks, email messages with attachments, Internet download, files transferred via FTP, IRC channels, P2P file sharing networks, etc.

cricri uses the following infection strategies:

• Resident: once it has been run, the virus goes memory resident and stops functions belonging to the operating system. Therefore, every time the operating system or an application tries to access any of these functions, the virus will activate and infect new files.
• Stealth: when the virus is memory resident, it hides the modifications made to the boot sectors or files it has infected. These modifications are: changes in size, date, attributes, etc.
• Polymorphic: it encrypts itself in a different way with each infection it carries out. In order to do this, it uses different keys and operations. As a result, the virus has different characteristics in each new infection, which makes it difficult for antivirus pro-grams to detect this virus.
• Encrypted: it encrypts its code in order to make it difficult to detect. In order to carry out its infection, the virus decrypts itself and, once infection has been carried out, it encrypts itself again.