Xolox have withdrawn their product, but it is easy to get it going again. If you operate behind a firewall then simply block the site http://www.xolox.nl. End of problem.
If you don't have a firewall, there are ways of doing the same thing. however I suggest you do get a firewall, as using these file-sharing utilities does advertise your IP address and this potentially attracts hackers. A good (free) firewall is ZoneAlarm.

I use Zonealarm Pro, yesterday Xolox was working fine, but when I restarted today, it came up with 'version has expired'. It let me carry on anyway after clicking OK. I've read some reports of not upgrading to 1.13 and turning off automatic install of new versions. I've always had automatically install newer version unchecked. So how do I block http://www.xolox.nl in my firewall? Or what's the key to keeping it work, it seems to be working fine at the moment?

Actually, although it was me who posted the advice to use a firewall, I think it is better to download the 1.13 "patch". This effectively does the same thing i.e. stops Xolox checking it's web-site and finding the expiry instruction.
If your Xolox is still working, then maybe you already have v1.13 or you have not tried a new search/download.

Interesting....I haven't changed anything. It still says 'Xolox version: 1.12' at the top, automatic updates are off and all searches still work fine...

Update: I couldn't download anything, only upload. Grabbed the 1.13 floating around (the hacked one), that seems to work a treat