Other popular CNET websites such as News.com, Gamespot and Gamefaqs were also unavailable during this time. Considering the downtime occurred in the evening in the US, and not in the middle of the night, it is unlikely to have been due to planned maintenance.
The downtime started just after 8:30 p.m. EST on Tuesday and lasted for about one hour and 13 minutes. Last time Download.com had a longer outage was back on August 31, when the website was unavailable for three hours and 15 minutes.
Detailed information can be found on these report pages:
(Timestamps are GMT+1.)
Incidents such as these (if it really was an incident, but it seems likely) show that not even large players such as CNET are immune against website problems.
Data source: Pingdom GIGRIB.