Is there any other confirmation of that?
Yes, Symantec have already confirmed this themselves…
Well… A very embarassing situation for a security company.
Are we only talking about signatures or the engine code was also compromised?
It was the source code from two earlier versions of their enterprise product and some documents. Well, that’s what the hackers have released to-date anyway. It wasn’t stolen directly from Symantec either, it was stolen from a 3rd party (Indian Military Intelligence). I think it’s all in the URL I posted.
Seems things got worse…
This coming Tuesday behold the full Norton Antivirus 1,7Gb source code.
http://news.yahoo.com/indian-hackers-offer-help-man-suing-symantec-061440036.html
Interesting HTML name Yahoo has there (indian-hackers-offer-help-man-suing-symantec.HTML)… it doesn’t mention that in the article. 
Ah, Yahoo’s HTML name seems to be tied the following Reuters release from yesterday…
[url=http://www.reuters.com/article/2012/01/13/us-symantec-hacker-idUSTRE80C1QW20120113]Hacker says will release Symantec source code[/url] [reuters.com]
… I’m surprised nobody else has picked up on this yet either. I wonder what else that guy/girl got off the Indian Military Intelligence servers?
The red telephone number ;D
Ooo… Batman will not be pleased. 
Looks like it happened with Kaspersky before. http://news.softpedia.com/news/Kaspersky-Confirms-Source-Code-Leak-Threatens-Legal-Action-Against-Downloaders-181456.shtml
Update: The hacker group/hacker “Yama Tough” that said they/he/she would release the full Norton source code today (all 1.7Gb* of it), have now said…
We've decided not to release code to the public until we get full of it =) 1st we'll own evrthn we can by 0din' the sym code & pour mayhem[url=https://twitter.com/YamaTough]source[/url] [twitter.com]
*I’m assuming they/he/she mean 1.7GB (Gigabyte) here, not 1.7Gb (Gigabit).