[Yukarasaki]

Some hacker group know as NoS apparently got ahold of a way to spam announcements in the client. If you clicked on any of the links in the announcements I urge you to disconnect from the internet and scan your computer. Simply closing the announcements shouldn't have done anything, but the links lead to keyloggers and several people have been infected already according the riot forums.

[Reiki]

Pinned, thanks for the notice.

[Nessah]

The links led to a site where you were forced to download and run a Java app. If you click "Run" on the Java pop up that was offered, it will download the keylogger into your Temp Files folder, and from there it would auto execute itself, messing up your computer aswell as registering keystrokes. If you didn't click Run on the box, you should be safe. But like Yukarasaki says, best is to pull the internet plug and do various virus searchs, for instance the Malwarebytes one. ( http://www.malwarebytes.org/ )