Janis Elsts

Normally when you login to your blog WordPress will create a session cookie that is used to authenticate you. If someone was to steal the cookie they would be able to use it to get full access to your blog without having to know your password. This plugin prevents that from happening – it makes the cookie specific to your IP address, so it won’t be usable from a different computer.
Use this plugin if you have a static IP. If you have a dynamic IP address and it changes often you will get logged out frequently.
A bit more info can be obtained from the <a href="http://w-shadow.com/blog/2008/07/12/safer-cookies-plugin-for-wordpress/" title="Safer Cookies homepage" rel="nofollow ugc">Safer Cookies homepage</a>

Safer Cookies

Ties the WP session cookie to your IP address so that it can't be used to get access to you blog from another computer.

Subhransu Sekhar

When you login to wordpress site it saves the auth info in cookies which have a expire time of 2 days. If some body get access of your cookie he can get into your wordpress iste. Use this plugin to increase the security by adding some random variable in the cookie for validation.

Safe Cookies

Secure your wordpress site by making the Auth Cookie more secure

Safer Cookies vs Safe Cookies