I would like to suggest that you should go for complete antivirus solutions that protects your from virus, trojan, malware, spyware and adware.
My pc was just infected by Trojan and this trojan simply copied the username and password of my ftp software start injection iframe injection inside my website pages.
All the websites were damaged. At the time of attack I was using separate freeware antivirus , malware and spyware. All the Free version just don't detect the threat.
Problem solved when I use complete antivirus solution that protects from every threat and the virus database is updated every time I run my pc. I am using Kaspersky Internet Security.
Hope this answered your question.