Recentley the Backdoor.Win32.Delf.ctk Trojan was discovered by Sunbelt Software that can take over your computer displaying the following message (Spelling Mistakes are not mine):

Surfing PORN, ADULT and some other kind of sites you like without this software is dangerows and threatens with infection of your computer by harmful viruses, adware, spyware, etc. You strongly need to update your software to avoid infection and losting information from your computer. Please complete procedure of software update;

The Trojan then presents you with a 900 Number that can cost up $3/Minute US ($1.50 Canadian).

If you don't already... keep your System Anti Virus up to date.