Complex sentence: However, if an IP address has been used only or mostly for vandalism over a long period of time, it may be subject to a very long block, up to a year and occasionally even longer, but is almost never blocked indefinitely.
Split into simpler sentences: However, if an IP address has been used only or mostly for vandalism over a long period of time, it is often included in the category. These IP addresses may be subject to very long blocks, up to a year and occasionally even longer, but are almost never blocked indefinitely.