The SSH protocol is widely used for secure remote terminal connections and file transfers between a client and a server running Unix and its derivatives.
The Trojan horse was discovered in OpenSSH versions 3.2.2p1, 3.4p1 and 3.4. The compromised software was first made available on an official download server on 30 July or 31 July, and from there was likely to have been copied to other download sites.
Trojan horse programs install backdoor programs that let attackers gain access to a computer. In this case the malicious code is run when the OpenSSH software is compiled by the user, the advisory warned. It allows arbitrary commands to be executed with the privileges of the compiling user.
Anyone who installed OpenSSH or offered it for download since 30 July should verify the authenticity of the software. The compromised OpenSSH versions can be identified by their incorrect MD5 checksums and PGP signatures.
More information on the Trojan horse and how to detect it can be found in the OpenSSH advisory www.openssh.com/txt/trojan.adv and an advisory sent out by the Computer Emergence Response Team (CERT) ( www.cert.org/advisories/CA-2002-24.html).