What is ipfilter.dat?
This is a simple text file that specifies IP ranges to block. The format is xxx.xxx.xxx.xxx - yyy.yyy.yyy.yyy
You can also use single IPs on a line (i.e. xxx.xxx.xxx.xxx). It ONLY supports blocks: it will ignore all text specified afterwards (such as what BLM and Tiny BLM does).
Do not pad IPs with 0s to ensure that it will work (i.e., write 64.12.15.0 not 064.012.015.000), though it is reported to work anyway.
Place it in %AppData%\uTorrent, and set ipfilter.enable to true in the Advanced.
To reload ipfilter.dat without restarting µTorrent, simple set ipfilter.enable to false, then to true again.