GEN:SID 1:610
Message RSERVICES rsh root
Summary This event is generated when an attempt to login as the superuser is attempted using rsh.
Impact Serious. If successful the attacker may have gained superuser access to the host.
Detailed Information This rule generates an event when a connection is made using "rsh" with the username "root". Such activity is indicative of attempts to abuse insecure machines with a known default configuration.

Some UNIX systems use the "rsh" daemon which permits remote "root" logins. This may allow an attacker to connect to the machine and establish an interactive session.
Affected Systems  
Attack Scenarios An attacker finds a machine with the "rsh" service running and connects to it, then proceeds to guess the "root" password
Ease of Attack Simple, no exploit software required
Corrective Action Investigate logs on the target host for further details and more signs of suspicious activity

Use ssh for remote access instead of rsh.

Deny remote root logins to the host, use a normal user and "sudo" or give the user the ability to "su" to root where appropriate.
Additional References Arachnids:
http://www.whitehats.com/info/IDS391
Rule References arachnids: 391