There are several possibilities how a clean and legitimate website may become infected:
- Website was exploited by some hacktoolkit which searches for vulnerable websites, and automatically infects them.
- Infection was inserted on the machine that is used to create/upload websites, which means that the author's/administrator's computer is infected.
- An attacker gained direct access to the website administration thanks to a weak or stolen access password.
We recommend to contact the administrator of such website.