Sedo, ParkingSite and similar services place pay-per-click ads on parked domains, optimize the sites to attract traffic, and split the resulting ad revenue with the domain owner. Sedo, which hosts more than 235,000 domains at 1&1 Internet, was first hit on Aug. 21. “The cluster for serving the websites for the Sedo parking program has been attacked by a Bot network or a sophisticated attacker since this afternoon,” a Sedo representative reported on the DomainState forum. “We are experiencing a SYN flood attack with spoofed IP addresses as the source. … To give you an idea of the size of the attack: We would need about 200 additional servers to handle the SYN traffic coming in.”

ParkingSite, a newer service affiliated with the popular DNForum.com, began experiencing problems on Aug. 24, and said it changed servers to deflect the attacks. The service is now hosted at Interland.

The success of domain parking services has helped the domain resale market evolve from a speculative venture into an industry with a defined business model, which is now attracting considerable interest from venture capital firms. The industry also has critics, who compare the ad-filled pages to digital litter, and say the practice has inflated domain prices with speculative purchases of hundreds of thousands of domain names.