Recent versions of Orbit Downloader, a popular Windows program for downloading embedded media content and other types of files from websites, turns computers into bots and uses them to launch distributed denial-of-service (DDoS) attacks, according to security researchers.Starting with version 220.127.116.11 released in December, the Orbit Downloader program silently downloads and uses a DLL (Dynamic Link Library) component that has DDoS functionality, malware researchers from antivirus vendor ESET said Wednesday in a blog post.The rogue component is downloaded from a location on the program's official website, orbitdownloader.com, the ESET researchers said. An encrypted configuration file containing a list of websites and IP (Internet Protocol) addresses to serve as targets for attacks is downloaded from the same site, they said.Orbit Downloader has been developed since at least 2006 and judging by download statistics from software distribution sites like CNET's Download.com and Softpedia.com it is, or used to be, a popular program.Orbit Downloader was downloaded almost 36 million times from Download.com to date and around 12,500 times last week. Its latest version is 18.104.22.168 and was released in May.In a review of the program, a CNET editor noted that it installs additional "junk programs" and suggested alternatives to users who need a dedicated download management application.When they discovered the DDoS component, the ESET researchers were actually investigating the "junk programs" installed by Orbit Downloader in order to determine if the program should be flagged as a "potentially unwanted application," known in the industry as PUA."The developer [of Orbit Downloader], Innoshock, generates its revenue from bundled offers, such as OpenCandy, which is used to install third-party software as well as to display advertisements," the researchers said, noting that such advertising arrangements are normal behavior for free programs these days."What is unusual, though, is to see a popular utility containing additional code for performing Denial of Service (DoS) attacks," they said.The rogue Orbit Downloader DDoS component is now detected by ESET products as a Trojan program called Win32\/DDoS.Orbiter.A. It is capable of launching several types of attacks, the researchers said.First, it checks if a utility called WinPcap is installed on the computer. This is a legitimate third-party utility that provides low-level network functionality, including sending and capturing network packets. It is not bundled with Orbit Downloader, but can be installed on computers by other applications that need it.If WinPcap is installed, Orbit's DDoS component uses the tool to send TCP SYN packets on port 80 (HTTP) to the IP addresses specified in its configuration file. "This kind of attack is known as a SYN flood," the ESET researchers said.If WinPcap is not present, the rogue component directly sends HTTP connection requests on port 80 to the targeted machines, as well as UDP packets on port 53 (DNS).The attacks also use IP spoofing techniques, the source IP addresses for the requests falling into IP address ranges that are hardcoded in the DLL file."On a test computer in our lab with a gigabit Ethernet port, HTTP connection requests were sent at a rate of about 140,000 packets per second, with falsified source addresses largely appearing to come from IP ranges allocated to Vietnam," the ESET researchers said.After adding a detection signature for the DLL component, the ESET researchers also identified an older file called orbitnet.exe that had almost the same functionality as the DLL file, but downloaded its configuration from a different website, not orbitdownloader.com.This suggests that Orbit Downloader might have had DDoS functionality since before version 22.214.171.124. The orbitnet.exe file is not bundled with any older Orbit Downloader installers, but it might have been downloaded post-installation, like the DLL component.This is a possibility, but it can't be demonstrated with certainty, Peter Kosinar, a technical fellow at ESET who was involved in the investigation, said Thursday. It might also be distributed though other means, he said.Adding to the confusion is that an older version of orbitnet.exe than the one found by ESET is distributed with Orbit Downloader 126.96.36.199. The reason for this is unclear since Orbit Downloader 188.8.131.52 also downloads and uses the DLL DDoS component. However, it indicates a clear relationship between orbitnet.exe and Orbit Downloader.The fact that a popular program like Orbit Downloader is used as a DDoS tool creates problems not only for the websites that it's used to attack, but also for the users whose computers are being abused.According to Kosinar, there is no rate limit implemented for the packets sent by the DDoS component. This means that launching these attacks can easily consume the user's Internet connection bandwidth, affecting his ability to access the Internet through other programs.Users who install Orbit Downloader expect the program to streamline their downloads and increase their speed, but it turns out that the application has the opposite effect.Orbit Downloader is developed by a group called Innoshock, but it's not clear if this is a company or just a team of developers. Attempts to contact Innoshock for comment Thursday via two Gmail addresses listed on its website and the Orbit Downloader site, as well as via Twitter, remained unanswered.The program's users also seem to have noticed its DDoS behavior judging by comments left on Download.com and the Orbit Downloader support forum.Orbit Downloder version 184.108.40.206 is generating a very high amount of DDoS traffic, a user named raj_21er said on the support forum on June 12. "The DDoS flooding is so huge that it just hangs the gateway devices\/network switches completely and breaks down the entire network operation.""I was using Orbit Downloader for the past one week on my desktop when I suddenly noticed that the internet access was pretty much dead in the last 2 days," another user named Orbit_User_5500 said. Turning off the desktop system restored Internet access to the other network computers and devices, he said.Since adding detection of this DDoS component, ESET received tens of thousands of detection reports per week from deployments of its antivirus products, Kosinar said.