I use XenForo for 2 years or so we've never stumbled upon security issues. However a day ago or so something happened and users visiting our forum from Android-phones get redirected to a fishing site (http://flash-2012.com) that uses Adobe Flash logo and says that your flash version is obsolete and need to be upgraded. Once an user agrees he get redirected to porno, warez and other things like that.
The bug is not present at devices other than Android phones: even on Samsung Galaxy Tab Tablet.
The forum is deployed at http://forum.amperka.ru. Just upgraded it from 1.1.0 to 1.1.3, it didn't help.
How this could be done and what should I do to fix this?