Viruses still plague many networks and not everyone is taking it lightly: U.S. colleges are getting tough on students with infected PCs, unplugging them and fining them, Associated Press reports.Back-to-back waves of devastating infections that spread quickly across the Internet during August crippled some college and high school networks just before the start of the fall semester. At the University of North Texas, technicians are removing viruses from roughly 16 computers every 90 minutes — plus assessing a mandatory $30 cleaning fee. Vanderbilt University found infections in computers of roughly one-fourth its returning 5,000 students. Stunned technicians shut off connections to nearly 1,200 computers they determined were infected and gradually restored service over the next several days after ensuring each machine was clean.