Google announced they have updated two of their webmaster guidelines documents to better describe ways you should not use redirects to trick or manipulate Google's search results.
The Sneaky redirects added examples, including an example of mobile redirects. Here they are:
- Search engines shown one type of content while users are redirected to something significantly different.
- Desktop users receive a normal page, while mobile users are redirected to a completely different spam domain.
The What is hacking or hacked content? document added a section on redirects that reads:
Hackers might inject malicious code to your website that redirects some users to harmful or spammy pages. The kind of redirect sometimes depends on referrer, user-agent, or device. For example, clicking a URL in Google search results could redirect you to a suspicious page, but there is no redirect when you visit the same URL directly from a browser.
This should all be pretty obvious to most of you but be careful with your redirects.
Forum discussion at Google+.