Find whether your site is infected (or) marked as malicious by Google?

Yes it happens.Even if you're most careful. Someone,somehow gets access to your hosting account and injects malicious code into your site that tries to compromise the experience of visitors to your site. Maybe its not even you but someone else who hosts with the same company which brings your web host into disrepute.

How do you find out?

Maybe you've had a complaint from a visitor, maybe your browser warns you your own website is not a safe site (or) you can periodically check from here :
Google Safe Browsing:

http://www.google.com/safebrowsing/diagnostic?site=http://yoursite.com/

where you replace yoursite.com with the web address of your website.

Result:

Example: EuBlogger

It displays a range of information including the status of your site, when it was last scanned, whether your site has distributed malicious software, whether you're in a bad Internet neighbourhood etc.

What do you do if you are?

You need to have a look at the code on your site, remove the malicious code and then change password to your hosting company (or even the hosting company itself) if it keeps reoccurring.

Now wouldn't it be nice if this was a default part of Google Webmaster tools. Maybe some day.

Thanks:Ausmdweb