This is not a trojan or a virus. Nastysex is a program to show pornographic images. We sometimes get queries about it, as it can easily cause substantial phone costs.
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The program is distributed in several different version from a wide range of XXX web sites. Filenames include SEXWARE.EXE and XXXFILES.EXE.
When installing the software, it explains that the software is going to call out with a modem to download pornographics pictures "from another country" as they are "too explicit to be stored in USA".
The user has a free choice to decline the offer. If he does, he gets this display:
If the user enters his user info and his modem's COM port, the software will call out to Guyana in Southern America (phone number: +592 279 156) and will download XXX pictures.
Although this can easily cause huge phone bills, the program does not try to hide the fact that it's going to call to another country. Thus, this is not a trojan and F-Secure Anti-Virus WILL NOT detect or stop this program.
[Mikko Hypponen, F-Secure]