In the last week or so, several security issues have been identified and repaired in DotNetNuke.  Today, DotNetNuke 4.8.3 was released to rectify these issues.

You can read the DotNetNuke Security Bulletins here.

DotNetNuke Corporation recommends that you upgrade your installations as quickly as possible.  If upgrading will take a while, there are steps outlined in the security bulletins that will mitigate the security problems.

For further info on security issues and the best way to deal with a security issue if you find one, have a read of these blog posts by various core team members:

DotNetNuke Security Notice
Security Lessons Learned
DotNetNuke Security Update
DotNetNuke Is a Secure Platform
It never rains but it pours