http://www.cert.org/advisories/CA-2002-24.html
I am still looking for the break-in that predates this breakin, my memory is fucking horrible. I apologize. It will take me a while for me to find it.
1) Main OpenBSD server wasn't compromised, main FTP server ("ftp.openbsd.org") was.
2) Source code (the one in CVS) wasn't compromised, only .tar.gz packages placed on the FTP server were.
3) They did want people to know about this, that's why they released security advisory [1].
On top of that, at the time "ftp.openbsd.org" wasn't even running OpenBSD, the FTP server was part of SunSITE powered by Solaris [2].
[1] http://marc.info/?l=openbsd-misc&m=102821528812161&w...
[2] http://www.openbsd.org/cgi-bin/cvsweb/www/faq/faq8.html.diff...