This is probably caused by the Swen.A virus.
F-Secure
http://www.f-secure.com/v-descs/swen.shtml

Network Associates:
http://vil.nai.com/vil/content/v_100662.htm

Trend Micro:
http://www.trendmicro.com/vinfo/virusencyclo/default5.asp?VName=WORM_SWEN.A

Symantec
http://securityresponse.symantec.com/avcenter/venc/data/w32.swen.a@mm.html

Computer Associates: (McAfee)
http://www3.ca.com/virusinfo/virus.aspx?ID=36939

Registry Repair Tool
http://a64.g.akamai.net/7/64/2015/2003-09-18-15-/download.nai.com/products/mcafe
e-avert/undo.reg

Removal tools
http://www3.ca.com/Files/VirusInformationAndPrevention/ClnSwen.zip
Warning: Before running ClnSwen.com, please ensure that you carefully
review the
ReadMe.txt instruction file that accompanies this utility.

And from Michael Jennings we have:

The BitDefender repair tool, available at the bottom of this page:
http://www.bitdefender.com/bd/site/virusinfo.php?menu_id=1&v_id=158#
will fix being blocked from regedit. I guess it gets the rest of Swen.

McAfee's stinger gets a variety, including Swen:
http://vil.nai.com/vil/stinger/

This site has tools, but there may be a long download delay:
https://www.europe.f-secure.com/v-descs/swen.shtml

Possibly Swen.  See
http://vil.nai.com/vil/content/v_100662.htm

Ben