Are there any virus for Linux?
I received a mail in KMail, but it says:" this is a html mail, it only display html source code for safety ..."

All OSes have vulnerabilities (viruses, security breaches, etc.).

So Linux can also have viruses.

If you do think there is a virus use an antivirus.

HTML email is not a virus, but a coded (in HTML) mail.

To answer your thread question, the answer is, YES.

As for HTML, lots of email applications are using that default caution these days because you can get hacked from something encoded in html, xml, jpeg, gif, flash, and just about anything. Microsoft went so far as to NOT accept ANY attachment by default using Outlook Express.

In the case of email I set my email accounts to display only people I have in my personal address book. If the mailer doesn't have this option I don't use it. But of course another option would be to run a mail program that didn't have anything set for file helpers and run it to change all incoming messages to plain text only. You can get hacked that way too if I'm not mistaken so I've stopped doing that too.

For email you can try Thunderbird or the emailer that comes with Netscape 7.2 or ... and for the virus problem, there are Linux virus removal and detection programs out there also.

Of course, Linux virus detection tools are primarily for catching Windows viruses that are contained in emails. Part of this is because there are practically no viruses written for Linux. (There are a handful, yes, but AFAIK, none has been able to successfully propagate in the wild.)

There are, I believe, some non-virus ways that crackers can damage your system via html-formatted email, as well as "spyware" (in this case, data-mining cookies).