Internet addiction disorder is used interchangeably with problematic Internet use, pathological Internet use, and Internet addictive disorder. In some cases, this behavior is also referred to as Internet overuse, problematic computer use, compulsive Internet use, Internet abuse, harmful use of the Internet, and Internet dependency. Physical symptoms include a weakened immune system due to lack of sleep, loss of exercise, and increased the risk for carpel tunnel syndrome and eye and back strain. Symptoms of withdrawal might include agitation, depression, anger and anxiety when the person is away from technology. These psychological symptoms might even turn into physical symptoms such as rapid heartbeat, tense shoulders and shortness of breath. According to David Hodgins, a professor of psychology at the University of Calgary, online gambling is considered to be as serious as pathological gambling. It is known as an "isolated disorder" which means that those who have a gambling problem prefer to separate themselves from interruptions and distractions. Because gambling is available online, it increases the opportunity for problem gamblers to indulge in gambling without social influences swaying their decisions. This is why this disorder has become more a problem at this date in time and is why it is so difficult to overcome. The opportunity to gamble online is almost always available in this century opposed to only having the opportunity in a public forum at casinos for example. Online gambling has become quite popular especially with today's adolescents. Today's youth has a greater knowledge of modern software and search engines along with a greater need for extra money. So not only is it easier for them to find opportunities to gamble over any subject, but the incentive to be granted this money is desperately desired. Video game addiction is a known issue around the world. Incidence and severity grew in the 2000s, with the advent of broadband technology, games allowing for the creation of avatars, 'second life' games, and MMORPGs (massive multiplayer online role playing games). World of Warcraft has the largest MMORPG community online and there have been a number of studies about the addictive qualities of the game. Addicts of the game range from children to mature adults. A well-known example is Ryan van Cleave, a university professor whose life declined as he became involved in online gaming. Andrew Doan, MD, PhD, a physician with a research background in neuroscience, battled his own addictions with video games, investing over 20,000 hours of playing games over a period of nine years. Online gaming addiction may be considered in terms of B.F. Skinner's theory of operant conditioning, which claims that the frequency of a given behavior is directly linked to rewarding and punishment of that behavior.