Last week, there were some serious security flaws in all available versions of the uTorrent client. Part of the errors allow code execution on the client running machine. Errors (in part) are corrected in version 3.5.3. We suggest that you (in your own interest) update your clients or look for other alternatives. We are planning to take more serious steps against older versions of uTorrent (banners). We'll get in touch with the exact details within a few days.