The biggest competitive gaming event of all time, Valve's $18 million Dota 2 tournament known as The International 2015, has been disrupted due to a distributed denial of service (DDoS) attack that crippled the event's internet connection.
This particular DDoS attack halted a best-of-three matchup between Evil Geniuses and compLexity Gaming for several hours as Valve technicians struggled to reduce the impact of the attack. After play resumed around 4:20pm ET, the match continued without further interruptions, although the attackers could attempt another DDoS attack before the tournament finishes on August 8th.
Dota 2 requires an internet connection to play, unlike some other competitive games that can simply be played over a local network. This means that if an attacker can find the location of the servers that run Dota 2, they can overwhelm them through a simple DDoS attack, putting a stop to any competitive play at the time.
There's not a whole lot a company can do to prevent a large scale DDoS attack from occurring, as attempts to filter out 'bad' traffic to a server may end up harming legitimate users. Once a server comes under fire from an attack, there are usually some steps a company can take to reduce the impact, although usually some damage has already been done before technicians get the situation under control.
It's odd that Valve relied on standard Dota 2 servers for the tournament, rather than creating a modified version of the game that used local severs isolated from the public internet. This is one option that Valve may explore to ensure that DDoS attacks don't interrupt their major e-sports events in the future.