Many people browse the web copying and pasting passwords and other personal information to their clipboards for convenience. They might have just signed up for a new service and copied the randomly created password from the registration email so they can sign in for the first time, or when they have forgotten their password. Unfortunately, the default settings in Internet Explorer make it easy for any malicious site to read your clipboard information, with a single line of code! Granted they won't have too much information unless your login and password was in the clipboard, but this is a security risk regardless.
The easiest solution comes in the form of a using better browser. However, for those requiring the use of Internet Explorer this can be remedied by either being careful on what you send to the clipboard while web browsing or turning up the security settings in IE's options and unchecking Allow Paste Operations via Script, as described.