The chkrootkit security scanner searches the local system for signs that it is infected with a 'rootkit'. Rootkits are set of programs and hacks designed to take control of a target machine by using known security flaws.
Types that chkrootkit can identify are listed on the project's home page.
Please note that where chkrootkit detects no intrusions, this does not guarantee that the system is uncompromised. In addition to running chkrootkit, more specific tests should always be performed.