How do I scan my Linux system for rootkits, worms, trojans, etc.?

Either with chkrootkit or with rkhunter.

chkrootkit

Either install the package that comes with your distribution (on Debian you would run

apt-get install chkrootkit

), or download the sources from www.chkrootkit.org and install manually:

wget --passive-ftp ftp://ftp.pangeia.com.br/pub/seg/pac/chkrootkit.tar.gz
 tar xvfz chkrootkit.tar.gz
 cd chkrootkit-<version>/
 make sense

Afterwards, you can move the chkrootkit directory somewhere else, e.g. /usr/local/chkrootkit:

cd ..
 mv chkrootkit-<version>/ /usr/local/chkrootkit

Now you can run chkrootkit manually:

cd /usr/local/chkrootkit
 ./chkrootkit

(if you installed a chkrootkit package coming with your distribution, your chkrootkit might be somewhere else).

You can even run chkrootkit by a cron job and get the results emailed to you:

Run

crontab -e

to create a cron job like this:

0 3 * * * (cd /usr/local/chkrootkit-<version>; ./chkrootkit 2>&1 | mail -s "chkrootkit output my server" [email protected])

That would run chkrootkit every night a 3.00h.

rkhunter

Download the latest rkhunter sources from www.rootkit.nl:

wget http://downloads.rootkit.nl/rkhunter-1.2.7.tar.gz
 tar xvfz rkhunter-1.2.7.tar.gz
 cd rkhunter/
 ./installer.sh

This will install rkhunter to the directory /usr/local/rkhunter. Now run

rkhunter --update

to download the latest chkrootkit/trojan/worm signatures (you should do this regularly).

Now you can scan your system for malware by running

rkhunter -c