>>
>>How the malicious script got into your page?
>
>I don't know. I would not added this type of a long script if my life depended on it <g>. The hosting company support person said that either someone hacked into my account (and he suggested I change my user name and password); or one of the computers I use for connecting to the site (I use CuteFtp) could have had the virus. I only use one computer (this one) where I have Avast installed. I will do a full scan tonight to see if Avast will find something. And I am also thinking about purchasing a commercial AV software, in addition to Avast. Actually yesterday I bought SpyBoot AV/Firewall software for my daughter's computer. Today is the 2nd day and she has not caught any virus on her PC yet <g>. She actually had Avast installed on her PC but it did't prevent her from catching some Trojan (from one of the music download sites).

If your site runs certain software such as phpBB, it may have become infected through a vulnerability. If you don't fix the vulnerability you'll just get infected again:

http://it.slashdot.org/it/08/03/17/2358207.shtml

There have been several cases of mass exploits lately.