An unpatched vulnerabiilty in Internet Explorer is actively being used by malicious attackers that can allow remote code execution on an exploited computer. This would allow a malicious web site to have the ability to execute commands on the remote computer using the same privileges as the logged in user. These commands could include having the compromised computer download and run other software or create accounts. As this vulnerability is currently unpatched it is strongly suggested that you switch to a browser such as Chrome or Firefox until a patch is created and released.
Microsoft has issued a Security Advisory (2757760) discussing this vulnerability and that they are investigating it. As this is a severe vulnerability, it is expected that Microsoft will release an out-of-band patch rather than waiting for a patch tuesday release.