Thanks for your information Skelator.
Remember that Microsoft do not send e-mails with updates (all of them are hoaxes or another kind of trap… >:(
See: http://www.avast.com/forum/index.php?board=2;action=display;threadid=1219;start=msg6620#msg6620
http://www.f-secure.com/v-descs/swen.shtml
http://www.sophos.com/virusinfo/analyses/w32gibef.html
http://www3.ca.com/virusinfo/virus.aspx?ID=36939
http://vil.nai.com/vil/content/v_100662.htm
http://securityresponse.symantec.com/avcenter/venc/data/w32.swen.a@mm.html
http://www.trendmicro.com/vinfo/virusencyclo/default5.asp?VName=WORM_SWEN.A
http://www.viruslist.com/eng/viruslist.html?id=88029

For worm (swen) see:
http://www.f-secure.com/v-descs/swen.shtml
http://www.sophos.com/virusinfo/analyses/w32gibef.html
http://www3.ca.com/virusinfo/virus.aspx?ID=36939
http://vil.nai.com/vil/content/v_100662.htm
http://securityresponse.symantec.com/avcenter/venc/data/w32.swen.a@mm.html
http://www.trendmicro.com/vinfo/virusencyclo/default5.asp?VName=WORM_SWEN.A
http://www.viruslist.com/eng/viruslist.html?id=88029

and avast! foruns:

http://www.avast.com/forum/index.php?board=1;action=display;threadid=1356;start=msg7695#msg7695
http://www.avast.com/forum/index.php?board=2;action=display;threadid=1335;start=msg7582#msg7582
http://www.avast.com/forum/index.php?board=2;action=display;threadid=1340;start=msg7577#msg7577
http://www.avast.com/forum/index.php?board=2;action=display;threadid=1348;start=msg7558#msg7558
http://www.avast.com/forum/index.php?board=4;action=display;threadid=1231;start=msg7523#msg7523http://www.avast.com/forum/index.php?board=2;action=display;threadid=1096;start=msg7382#msg7382
http://www.avast.com/forum/index.php?board=2;action=display;threadid=1296;start=msg7111#msg7111
http://www.avast.com/forum/index.php?board=2;action=display;threadid=1282;start=msg7014#msg7014

Swen is a really anoying worm :cry: