According to the company website and other reports on the web, registrar Network Solutions experienced a distributed denial of service (DDOS) attack today that brought down it’s DNS services.  Any website using DNS services or hosting from NSI could have been down as a result of the attack.  The official post on the NSI blog stated :

There may be some latency on Network Solutions DNS Severs and some queries may be timing out.  This may include instances when someone types a domain name into a browser and the website will temporarily not resolve.

According to Circle ID the attack occured over the last 48 hours.  Company spokesperson Shashi Bellamkonda posted that the company was working to mitigate the attack and speedup DNS queries.