f a person goes to prison for using a computer and the Internet to commit a crime, can he be barred from using the Internet after the sentence is served?

Courts are increasingly facing the question as the Internet age gives rise to an explosion of cybercrime. But appellate courts in different parts of the country are coming up with different answers. And in the process, they are showing how an emerging technology can cause rifts in the legal landscape and pose difficulties in monitoring offenders.

The United States Court of Appeals for the Fifth Circuit, whose opinion interprets law in Louisiana, Mississippi and Texas, has ruled that people on probation may be barred from using computers and the Internet. The court argued that while this prohibition can greatly restrict a person's freedom and ability to find work, it also protects society from criminals who have turned the computer into a weapon.

But two other federal appeals courts, including the one governing New York, have recently concluded that such a prohibition is too broad. In overturning the sentence of a child pornographer last year, the Court of Appeals for the Second Circuit ruled that the Internet was as vital to everyday existence as the telephone and that while the government could monitor an offender's computer use, it could not stop it completely.

And the Court of Appeals for the Third Circuit, which covers New Jersey and Pennsylvania, has issued conflicting opinions in cases involving child pornography. In one case in 2000, it allowed a complete ban to stand, saying that it was necessary to deter a public threat to children. But in another — issued earlier this month — it argued that such a condition was overly broad. In this case the court said these sentences would have to depend on the facts in each individual case.

The courts have noted that computers now pervade virtually every area of life, suggesting a reason they have found a complete ban excessive, said Jennifer S. Granick, director of the Stanford Center for Internet and Society.

"Computers are everywhere," she said. "The A.T.M. is a computer; the car has a computer; the Palm Pilot is a computer. Without a computer in this day and age, you can't work, you can't communicate, you can't function as people normally do in modern society."

The issue emerges just as Kevin Mitnick, the hacker once called by the government "the most-wanted computer criminal in U.S. history," is poised to start using the Internet again. Mr. Mitnick served five years for breaking into computer networks of major corporations and stealing software; he was released from prison in January 2000. As a condition of his probation, he has not been allowed to use the Internet — a restriction that expires today.

Differences of opinion among federal courts are not unusual, though this rift can mean that two people living in different states may receive different sentences, even if they commit similar crimes. But the offenders are not the only people directly affected by the changing landscape.

The impact has been felt, too, by probation officers, whose job it is to monitor offenders' activities after they are released from prison. Where they cannot rely on a complete Internet ban, probation officers are being forced to pioneer ways to make sure that offenders on probation or on supervised pretrial release do not use computers and the Internet to commit new crimes.

That has meant finding technologies to monitor what Web sites offenders visit and what e-mail messages they send.

"This made our jobs more difficult," Brian Kelly, a federal probation officer in New York, said of the decision last spring in the case of Gregory Sofsky by the Federal Court of Appeals for the Second Circuit, which includes New York, Connecticut and Vermont. Initially, Mr. Sofsky, who was convicted of receiving child pornography on his home computer, was sentenced to 10 years in prison, after which he would not be allowed to use the Internet for three years.

His successful appeal means not only that he will be allowed to use the Internet after his release from prison, but that sentences prohibiting Internet use were invalid for other offenders, too. The ruling has resulted in modified sentences for at least seven other people in the region, who were originally prevented from using computers while on supervised release — a term that can refer to probation or pretrial release.

Under the modified sentences, they still cannot use computers or the Internet at will. They are restricted in what Web sites they can see, chat rooms they can visit, and people they can associate with online.

In the Eastern District of New York, which includes Brooklyn, Staten Island, Queens and Long Island, the job of monitoring has fallen to Mr. Kelly and several colleagues, who employ technologies that let them observe an offender's computer activity remotely. For instance, they have installed software on several offenders' computers that lets them dial into an offender's computer and get a log of Web surfing and other online activities.

"I see every e-mail, every chat, every instant message," Mr. Kelly said recently, while sitting in his office, bringing the log onto his screen. "This person was on Google at 8:15. Here's an e-mail he received earlier today."

Mr. Kelly is planning over the next 60 days to add biometric fingerprinting equipment, which scans a person's fingerprint before allowing access to a computer. Mr. Kelly said the technology would help him know exactly who was logged on to a computer, and thus prevent an offender from asserting that an illegal activity, like downloading child pornography, took place when someone else was using the computer.

The monitoring technology is still far from foolproof, Mr. Kelly said, noting that a sophisticated computer user can probably find ways to evade it. Still, he said that he received calls "once or twice a week" from jurisdictions around the country looking to start or upgrade their computer supervision efforts.

Some other jurisdictions are using decidedly less high-technology methods. Ms. Granick, the professor at Stanford, who is a lawyer and has defended computer hackers, said she came upon some methods of restricting her clients' use that are not foolproof. In one case, she said, a San Diego man accused of hacking into corporate computers was put on pretrial release and told not to use the Internet. The way the government enforced the restriction was by putting black and yellow police tape on the computer to ensure he did not attach an Internet connection.

But even the high-technology monitoring methods leave much to be desired, said Scott Charney, chief security strategist for Microsoft and a former federal prosecutor who headed the computer crime and intellectual property section for the Justice Department. They "can be easily circumvented," he said, noting, for example, that a child pornographer could find ways to use the computer to obtain, then eliminate, offending images before being caught. "If a guy is technically sophisticated, he can delete and wipe away all the files."

Still, Mr. Charney added that from a legal standpoint, there is a very good reason to sentence people to limited Internet access "even if the technology is not there to enforce it." He said the sentence was an important deterrent because an offender knows that if he is caught, he will go back to prison without getting another trial.

Ross Nadel, chief of the division of computer hacking and intellectual property for the United States attorney for Northern California, said he believed that good reason still existed in certain cases to sentence offenders to a complete Internet ban. And he argued that banning someone from the Internet was not the same as banning someone from use of the telephone.

"There are not cases where people are using the phone to harm sensitive computer networks," he said, asserting that computers and the Internet have become integrated and inseparable in some cases from the crime.

The views of the Second Circuit Court of Appeals and the Fifth Circuit Court of Appeals, covering Louisiana, Texas and Mississippi, show the differing reasonings being applied. In the Sofsky case in the Second Circuit, the court granted that allowing Mr. Sofsky access to the Internet could "facilitate his continuation of his electronic receipt of child pornography."

But the court said that not allowing Mr. Sofsky to use the Internet would prevent him access to e-mail, "an increasingly widely used form of communication," and prevent his performing tasks like getting a weather forecast or reading a newspaper online. The ban, it said, "inflicts a greater deprivation on Sofsky's liberty than is reasonably necessary."

In May 2001, the Fifth Circuit reasoned differently in the case of Ronald Scott Paul, a Texas man who was caught in 2000 with a large number of child pornography images on his computer. According to court records, Mr. Paul also had fliers advertising himself as a lice-removal specialist who would spray children for lice, a process that would require children to undress completely.

In its sentence, a lower court ruled that when Mr. Paul was released from prison, he should not only be prohibited from using the Internet, but even a computer. In its ruling, the Fifth Circuit court agreed, noting Mr. Paul used the Internet to exploit children and seek out "boy lovers."

The Internet and computer ban "is reasonably related to Paul's offense and to the need to prevent recidivism and protect the public," the court ruled.

The rift among the courts may not be resolved any time soon, Mr. Charney of Microsoft said. He said such differences are not uncommon, particularly in an emerging area of law. In this case, he said, he would not be surprised to see the split continue for many years.