Security: Somebody wants hack my joomla web site

I have been discovering suspect users are register in a corporate web site developed by me.
This problem is coming about five month .

Why are they suspect?. If you see the below list, you can look the values of the register fields “Name” and “Username” are equals, example Name=” idiodiend idiodiend” and Username ”idiodiend”.

It looks like an automatic attack by robots (bots register) or spammers . I ´m worried about it. I have fear that anybody could robs the joomla administrator password or ftp account.

I have installed CB 1.2 with captcha and four language pack.

I don´t know if it is a bug CB 1.2 ? How I can resolve it?.

My joomla version is 1.5.15

Example:
Name Username
VilliamYH VVilliamYH VVilliamYH Registered tymnbonopinoLup@mailtoo.bij.pl 05/01/2010 10:01:32
idiodiend idiodiend idiodiend Registered disruptivz@gmail.com
05/24/2010 10:18:27
anassydrums anassydrums anassydrums Registered l.a.urelwestmanoce@gmail.com 06/10/2010 06:08:33
Snitteekibtal Snitteekibtal Snitteekibtal Registered nantrennae@lvivs.com
06/15/2010 18:39:38
zerrierlookek zerrierlookek zerrierlookek Registered scopyjoyday@ramireschat.com 06/18/2010 09:15:30
limisuti1985 limisuti1985 limisuti1985 Registered vwymnvxvh54@kamelot-clan.com 06/21/2010 06:44:54
SweernSenia SweernSenia SweernSenia Registered armandpo.well.jy@gmail.com
06/21/2010 20:57:06
Staisizappy Staisizappy Staisizappy Registered tymnarernp@babusya.com
06/22/2010 19:50:14
Nedincink Nedincink Nedincink Registered nornnoneype@uaclub.net
06/23/2010 12:16:23
abnotamok abnotamok abnotamok Registered wrellavaklye@kinozal.tv
06/23/2010 19:35:30
FexySiminainy FexySiminainy FexySiminainy Registered usadswraripaf@babusya.com
06/25/2010 13:15:37
FampheappygeR FampheappygeR FampheappygeR Registered creankcex@peugeot-club.org 06/27/2010 19:34:52

Those aren't hack attempts nor can they steal your password, once the password is saved it's encrypted and can not be reversed, ever. Those are simply spammers. I recommend becoming a document subscriber for the latest CB Captcha plugin so you can have captcha protection on registration. I also recommend upgrading to CB 1.2.3. You could also use Confirm (see CB configuration on the registration tab) to require registered users to confirm their email address and then those bots won't even be able to login as typically the emails are fake.