A shadowy figure sits alone in a room, his face dimly lit by a computer screen. With a grin, he types in a series of computer commands, and in the blink of an eye, someone's bank account is drained to zero.

In today's digital age, cyberattacks like this happen thousands of times per day. Hackers can steal money, information, or completely take control of a machine from anywhere in the world. However, not all hackers are villains.

Some hackers, called white hat or ethical hackers, are individuals who make the most of their hacking skills to identify security vulnerabilities（漏洞） in hardware, software and networks. Their job is crucial in preventing cyberattacks and safeguarding sensitive information. The term "white hat" originated from old cowboy movies, where heroes wore white hats and villains wore black ones. Like the heroes in cowboy movies, white hats seek to stop the bad guys and save the day.

White hat hackers only seek vulnerabilities legally, often working on open-source software or with authorized access to systems. Once these weak spots are identified, companies or individuals can take steps to prevent serious breaches and losses. White hat hackers use a variety of different techniques to keep the internet safe. Penetration testing, for example, allows them to mimic cyberattacks and uncover system weaknesses. Security scanning tools allow white hats to identify holes in a network's security systems. Simulating denial-of-service attacks （DoS attacks）helps companies prepare for attacks against their websites.

Many of the world's top white hat hackers began their journeys on the wrong side of the law. A prime example is Kevin Mitnick. This notorious hacker once held the title of "most wanted hacker" in the U. S. due to his cybercriminal activities in 1995. However, after being arrested and spending five years in jail, his life took a remarkable turn. Mitnick decided to use his hacking skills for ethical purposes, eventually establishing his own cybersecurity consulting company.

If you aspire to be a white hat hacker, start by building a strong foundation in computer and network fundamentals. Good luck, computer cowboy!

The Mona Lisa is the famous Leonardo da Vinci painting of a woman with a mysterious smile. This week, the painting gave up a secret.

Scientists used X-rays to examine the chemical organization of an extremely small part of the more than 500-year-old painting. The researchers discovered a technique Leonardo used in the work. A team in France and Britain discovered an oil paint used for the Mona Lisa was a special, new chemical mixture. It suggests that the Italian artist may have been in an experimental mood when he set to work on the painting early in the 16th century.

"He was someone who loved to experiment, and each of his paintings is completely different technically," said Victor Gonzalez. He is the study's lead writer. "In this case, it's interesting to see that indeed there is a specific technique for the ground layer of the Mona Lisa," he said in an interview with The Associated Press. Specifically, the researchers found a rare compound, plumbonacrite (水蛭石), in Leonardo's first layer of paint. The discovery, Gonzalez said, proved that da Vinci most likely used lead oxide to thicken and help dry his paint.

The scientists looked into its atomic structure using X-rays in a synchrotron (同步加速器). The machine moves particles at close to the speed of light, permitting researchers to look deeper into the paint structure. "Plumbonacrite is really a fingerprint of his recipe," Gonzalez said. "It's the first time we can actually chemically prove it."

Dutch artist Rembrandt may have used a similar mixture when he was painting in the 17th century. Gonzalez and other researchers have found plumbonacrite in his work, too. "It also tells us that those recipes were passed on for centuries," Gonzalez said. "It was a very good recipe."

But the Mona Lisa and additional works by Leonardo still have other secrets to tell. "There are plenty, plenty more things to discover," Gonzalez said. "What we are saying is just a little brick more in the knowledge."

A hobby is a regular activity that is done for enjoyment, typically during one's leisure time. By continually taking part in a particular hobby, one can acquire practical skill and knowledge in that area. Is travel a good hobby? Travel, in the youngest sort, is a part of education and, in the elder, a part of experience. Some may think otherwise. To them, visiting churches, castles, libraries, etc. is an absolute wastage of time. They may further say that one can read the account of these or see the films of the important places of the world. They forget that touch of actuality gives a different type of sensation and satisfaction.

Travelling may be an expensive hobby but it makes up for the financial loss. If a traveller has interest in life and its manifestations (表现), one can find much to keep oneself absorbed and happy. A student of any stream can definitely find something of his own interest and studies. One can definitely find everything that satisfies his cravings for knowledge and feelings.

As a hobby, travelling keeps us busy during leisure time; it is the best method to make use of time. Till a person breaks from dull routine, physically and mentally, one cannot find satisfaction. Travelling helps us to achieve this break. At a new place, one is curious to know and eager to gather all the unknown information about the place which he has neither read nor heard before and he gets thrills and surprises which keep the interest and enthusiasm alive and encourage us to keep our-journey on.

While travelling, one comes across a number of people from varied backgrounds and places. By interacting with them, he comes to know about their traditions also. In case one has ps ychological bent of mind, one increases one's experience and power to understand others. Understanding human nature is, perhaps, the best part of education. Travelling satisfies all demands of a good hobby--it is absorbing education and refreshment to the mind, body and soul.