Possible hijacking help

I have been looking at the logs for my various webservers and have noticed some "polling" going on that looks suspicious:

I have had one server up for about 3days now on 8080 and roughly every hour I recieve a request like: (note: that is not my domain, someone entered that themselves)
"GET http://hacker.org.ru/prxjdg.php"
yes, with the http in there and everything. That server is created of my own hand so I know exactly how it handles it.

So then I thought to check my iis server on port 80, and it's got wierder requests.
A common offending line: (I have nothing called mamba....)
Should I be worried about this? IIS is returning 404 errors for it, but is there harm in these things?
Any thoughts?

Thanks

PS: If this is the wrong place to post, feel free to move it to where it needs to be

re: Possible hijacking help

For what is worth, often these things happen when hackers try to sabotage a site by entering a query where you use sql, eg a search function. If have any doubts about the cleanliness of your box, it may be worth checking this at a quiet period. Often the intention is to bring a site down with the sheer amount of activity, so would suggest searching for ways to minimise this risk. HTH.