Attackers have compromised more than 25,000 digital video recorders and CCTV cameras and are using them to launch distributed denial-of-service (DDoS) attacks against websites.One such attack, recently observed by researchers from Web security firm Sucuri, targeted the website of one of the company's customers: a small bricks-and-mortar jewelry shop.The attack flooded the website with about 50,000 HTTP requests per second at its peak, targeting what specialists call the application layer, or layer 7. These attacks can easily cripple a small website because the infrastructure typically provisioned for such websites can handle only a few hundred or thousand connections at the same time.The Sucuri researchers were able to tell that the traffic was coming from closed-circuit television (CCTV) devices -- digital video recorders (DVRs) in particular -- because most of them responded to HTTP requests with a page entitled "DVR Components Download."Around half of the devices displayed a generic H.264 DVR logo on the page, while others had more specific branding such as ProvisionISR, QSee, QuesTek, TechnoMate, LCT CCTV, Capture CCTV, Elvox, Novus, and MagTec CCTV.The botnet seems to have a global distribution, but the countries with the largest number of compromised devices are Taiwan (24 percent), the U.S. (16 percent), Indonesia (9 percent), Mexico (8 percent), Malaysia (6 percent), Israel (5 percent), and Italy (5 percent).It's not clear how these devices were hacked, but CCTV DVRs are notorious for their poor security. Back in March, a security researcher found a remote code execution vulnerability in DVRs from more than 70 vendors. In February, researchers from Risk Based Security estimated that more than 45,000 DVRs from different vendors use the same hard-coded root password.However, hackers knew about flaws in such devices even before these disclosures. Back in October, security vendor Imperva reported seeing DDoS attacks launched from a botnet of 900 CCTV cameras running embedded versions of Linux and the BusyBox toolkit.Unfortunately, there's not much that the owners of CCTV DVRs can do, because vendors rarely patch identified vulnerabilities, especially in older devices. A good practice would be to avoid exposing these devices directly to the Internet by placing them behind a router or firewall. If remote management or monitoring is needed, users should consider a deploying a VPN (virtual private network) solution that allows them to connect inside the local network first and then to access their DVR.