Any one who is a webmaster will know of the headache caused by a malware infection on a website. The worst part of malware is that you will never know your website code is infected unless you go through your website code on a regular basis. You only come to know of this malice when your website traffic drops all of a sudden or search engines flag your website listing with a message like as follows:
or if you are using Google Chrome you may get a message like this on your browser
There are a number of websites which can check your website online for malware and inform you whether your website is safe for visitors or not.
I hope the above helps you. If you have any question/comments regarding the above then please let me know.