It simply means your website is compromised.
A compromised website is one that has been accessed by someone other than you. That someone has figured out your password (without your knowledge or consent) and was able to log in to your website. Can you afford to neglect this?
What are malwares?
The term "malware" covers all sorts of malicious software designed to harm a computer or network. Kinds of malware include (but are not limited to) viruses, worms, spyware, and Trojan horses.
If your website is compromised by hackers, they may decide to upload malicious scripts to your site in an effort to infect visitors to your site with viruses or other malicious software. If this happens and Google indexes your site, they may detect these malicious scripts and assign a warning to your website that will show up next to any search results for your website.
Solution
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Ensure that your code is free from such kind of vulnerabilities.
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Change all the FTP passwords regularly and keep good passwords that use a combination of alphabets + numbers + special characters.
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Before updating the new password in their FTP clients, perform a full system virus scan with a reliable virus scanner updated with the latest virus definition files.
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Also try not to save (remember) the FTP username/password on FTP clients or public computers.
Tips & Warnings
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Always keep a backup of your website with you.
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Your anti- virus should be reliable and updated regularly to the latest version.
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Choose good passwords.
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Choose your third-party support providers very carefully. Professional companies ensure their computer system is clean and do not compromise passwords. Alternatively, you can change the passwords once your designers and maintenance providers have completed the entrusted task.
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If you're considering installing an application provided by a third party, such as a widget, counter, or ad network, be sure to exercise due diligence.
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Contact your hosting company or publishing platform for support. Most companies have helpful and responsive support groups and/or security pages. If a security page or site has an RSS feed, subscribe to it to make sure you stay up to date.
Next Step
Once you're certain your site is free of malware, you can ask Google to review it. Google's automatic systems will scan your website. If no malware is found, they will remove the warning from your site. This may take a day or so to happen. If you've cleaned your site, but the warning is still in place after a couple of days, you may not have found and removed all the problematic content on your site.
