I first used chkrootkit recently. It categorised certain files of mine as suspicious. I understand that it did so because those files were hidden ones, but were not in my home directory. Many of the files chkrootkit called suspicious were connected with earlier kernels that I hadn't uninstalled, so I uninstalled those kernels. That reduced chkrootkit's list of suspicious files significantly. One of the files still on the list was associated with Firefox v 1.0.4. (I use Firefox 1.0.7.) On investigation, I found that in /usr/lib I had three directories, each connected with a version of Firefox earlier than the current one. Is there any risk involved in deleting the three directories?