HTML_Iframe.CV is the Trend Micro detection for Web pages that were compromised through the insertion of a certain iFrame tag. As of this writing, the affected Web pages are adult sites.

Once an unsuspecting user visits an affected Web page, this HTML iFrame connects to the Web page http:// {BLOCKED} to download a malicious JavaScript. Trend Micro detects this JavaScript as JS_DLOADER.NUF. As a result, routines of the downloaded script are also exhibited on the affected system.

Technical details can be found at this Trend Micro page.