phplinkdirectory "top hits" cheating

After analyzing the apache logs of my phplinkdirectory, I found some weird requests. After digging more into the problem, it seems like people click their own links or use automated software to do so, so in case you sort your directory listings by the number of visits/clicks they will get top positions in their category and also a top permanent spot in the "top hits" section. Basically they play with cl.php and use their id. And they do this from different IP addresses using proxies.