Perhaps you are running an old unpatched version of JBoss with a known WORM virus, which apparently modifes crontab to keep installing itself.
The following links I found in Google could be useful:
Thanks Dude. Turns out the server is infected with the worm. Will follow these links to clean it out and secure it. We just recently started using Oracle Linux, so did not see this on previous installations of Jboss.