This is an antibot client, no modern bot can connect to it. trying to inject a bot in it will get you deleted straight away. WARNING! Use any other client/program to play DarkOT than this official client may/will get your accounts deleted!
Download the DarkOT client
The file you download is a .zip file(packed), you can unpack it on any windows system by right click on it and select "extract all".
If you are afraid there's virus in it, feel free to look it up yourself!
You can upload files to Virustotal.com and scan them there! or any other virus scan services you could possible find by using google. https://www.virustotal.com/ Scan of the latest client released: VirusTotal -Scan (Without Minimap) VirusTotal -Scan (With Minimap)
Some of the scans will show some sort of "trojan", it's a false positive, it detects the part of the client that keep the client auto-updated.
It's nothing to worry about, if you still worry, ask someone who's experienced in viruses about their guidance in the subject.
If your antivirus would happen to detect the client as a virus, you have a poorly made antivirus that detect false positives, in that case add the client as an exception in the antivirus.
In general, most players wont have any problems with their anti-viruses on this subject.