Hyper-Threading technology, as used in FreeBSD and other operating systems that are run on Intel Pentium and other processors, allows local users to use a malicious thread to create covert channels, monitor the execution of other threads, and obtain sensitive information such as cryptographic keys, via a timing attack on memory cache misses.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A9747
http://www.vupen.com/english/advisories/2005/3002
http://www.vupen.com/english/advisories/2005/0540
http://www.securityfocus.com/bid/12724
http://www.redhat.com/support/errata/RHSA-2005-800.html
http://www.redhat.com/support/errata/RHSA-2005-476.html
http://www.kb.cert.org/vuls/id/911878
http://www.daemonology.net/papers/htt.pdf
http://www.daemonology.net/hyperthreading-considered-harmful/
http://sunsolve.sun.com/search/document.do?assetkey=1-26-101739-1
http://securitytracker.com/id?1013967
http://secunia.com/advisories/18165
http://secunia.com/advisories/15348
http://marc.info/?l=openbsd-misc&m=110995101417256&w=2