Just got hacked

[Devanand]

Hello,

I just opened my calendar and for today where should be birthdays I have message:

Hacked By: CrAcKeR-BeSi: 24-10-2009
Hacked By: CrAcKeR-BeSi: 24-10-2009
<meta HTTP-EQUIV="REFRESH" content="0; url=http://villarustica.com.mk/": 24-10-2009

this message is also showen in events on home page.

When you click on todays date you could see this:

http://i34.tinypic.com/35ba17b.jpg

Is this serious and where is hole. How can I prevent from this?




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Edit :

I found this line in my headinclude:

<meta name="description" content="$vboptKalendar
Hacked By: CrAcKeR-BeSi: 24-10-2009
Hacked By: CrAcKeR-BeSi: 24-10-2009
<meta HTTP-EQUIV="REFRESH" content="0; url=http://villarustica.com.mk/": 24-10-2009 ions[description]" />


How did they menage to put it there?