Unknown to most of them, their problem began when international hackers ran an online advertising scam to take control of infected computers around the world. In a highly unusual response, the FBI set up a safety net months ago using government computers to prevent Internet disruptions for those infected users. But that system will be shut down July 9 -- killing connections for those people.

The FBI has run an impressive campaign for months, encouraging people to visit a website that will inform them whether they're infected and explain how to fix the problem. After July 9, infected users won't be able to connect to the Internet.

LONG ARM OF SCOFFLAW

An online ad scam is having some unintended ramifications: The fix may prevent as many as 360,000 from getting online. Several sites will show if you're infected:

DNS Changer Working Group: can discern whether you’re infected and explain how to fix the problem.

DNSChanger Eye Chart: if the site goes red, you’re in harm’s way. Green means clean.

The FBI website: type in the IP address of your DNS server to find out if it is infected.

Read more on how to stay safe

On Tuesday, May 22, Google announced it would throw its weight into the awareness campaign, rolling out alerts to users via a special message that will appear at the top of the Google search results page for users with affected computers, CNET reported. 

“We believe directly messaging affected users on a trusted site and in their preferred language will produce the best possible results,” wrote Google security engineer Damian Menscher in a post on the company’s security blog.

“If more devices are cleaned and steps are taken to better secure the machines against further abuse, the notification effort will be well worth it,” he wrote.

The challenge, and the reason for the awareness campaigns: Most victims don't even know their computers have been infected, although the malicious software probably has slowed their web surfing and disabled their antivirus software, making their machines more vulnerable to other problems.

Last November, when the FBI and other authorities were preparing to take down a hacker ring that had been running an Internet ad scam on a massive network of infected computers, the agency realized this may become an issue.

"We started to realize that we might have a little bit of a problem on our hands because ... if we just pulled the plug on their criminal infrastructure and threw everybody in jail, the victims of this were going to be without Internet service," said Tom Grasso, an FBI supervisory special agent. "The average user would open up Internet Explorer and get `page not found' and think the Internet is broken."

On the night of the arrests, the agency brought in Paul Vixie, chairman and founder of Internet Systems Consortium, to install two Internet servers to take the place of the truckload of impounded rogue servers that infected computers were using. Federal officials planned to keep their servers online until March, giving everyone opportunity to clean their computers.

But it wasn't enough time.

A federal judge in New York extended the deadline until July.

Now, said Grasso, "the full court press is on to get people to address this problem." And it's up to computer users to check their PCs.

'We started to realize that we might have a little bit of a problem on our hands...'

- Tom Grasso, an FBI supervisory special agent

This is what happened:

Hackers infected a network of probably more than 570,000 computers worldwide. They took advantage of vulnerabilities in the Microsoft Windows operating system to install malicious software on the victim computers. This turned off antivirus updates and changed the way the computers reconcile website addresses behind the scenes on the Internet's domain name system.

The DNS system is a network of servers that translates a web address -- such as http://www.foxnews.com -- into the numerical addresses that computers use. Victim computers were reprogrammed to use rogue DNS servers owned by the attackers. This allowed the attackers to redirect computers to fraudulent versions of any website.

The hackers earned profits from advertisements that appeared on websites that victims were tricked into visiting. The scam netted the hackers at least $14 million, according to the FBI. It also made thousands of computers reliant on the rogue servers for their Internet browsing.

When the FBI and others arrested six Estonians last November, the agency replaced the rogue servers with Vixie's clean ones. Installing and running the two substitute servers for eight months is costing the federal government about $87,000.

The number of victims is hard to pinpoint, but the FBI believes that on the day of the arrests, at least 568,000 unique Internet addresses were using the rogue servers. Five months later, FBI estimates that the number is down to at least 360,000. The U.S. has the most, about 85,000, federal authorities said. Other countries with more than 20,000 each include Italy, India, England and Germany. Smaller numbers are online in Spain, France, Canada, China and Mexico.

Vixie said most of the victims are probably individual home users, rather than corporations that have technology staffs who routinely check the computers.

FBI officials said they organized an unusual system to avoid any appearance of government intrusion into the Internet or private computers. And while this is the first time the FBI used it, it won't be the last.

"This is the future of what we will be doing," said Eric Strom, a unit chief in the FBI's Cyber Division. "Until there is a change in legal system, both inside and outside the United States, to get up to speed with the cyber problem, we will have to go down these paths, trail-blazing if you will, on these types of investigations."

Now, he said, every time the agency gets near the end of a cyber case, "we get to the point where we say, how are we going to do this, how are we going to clean the system" without creating a bigger mess than before

That is the theory. But in practice, any protection the law offers investors could be difficult to enforce, according to lawyers trying to protect their corporate clients against the upheaval sure to follow if Greece defaults on its debts and adopts a new currency. So their advice is blunt: Remove cash and other liquid assets from Greece and prepare to take a short-term hit on any other investments. “My personal view is that it is irrational for anyone, whether a corporation or an individual, to be leaving money in Greek financial institutions, so long as there is a credible prospect of a euro zone exit,” said Ian Clark, a partner in London for White & Case, a global law firm that has a team of 10 attorneys focusing on the issue. Several multinational corporations have already taken the same view. Vodafone, the mobile phone operator, and GlaxoSmithKline, the pharmaceuticals firm, say they are “sweeping” money out of Greece and into British banks each evening. This applies not just to Greece but to most other euro nations, although Glaxo says it still keeps money in Germany. Corporate attorneys say looking to E.U. law provides only approximate guidance on whether Greece could stop using the euro while remaining in the Union. Although the E.U. prides itself on basing decisions on strict interpretation of the legal texts in its governing treaty and other legislation, the rules on euro membership have proved flexible. For example, while all 27 E.U. nations are supposedly obliged to join the single currency, once they meet certain economic criteria, Britain and Denmark were able to negotiate the option of retaining their own currencies. Sweden is one of the nations technically obliged to join the euro, but since a national referendum opposed the idea in 2003, no one has pressed the country to do so. Similarly, while leaving the euro might, legally, mean quitting the union itself, most experts see this as a technicality that can be circumvented as well. “The treaty doesn’t cover the question of what would happen if a country were to leave the euro and return to its previous currency,” said Stephen Weatherill, Jacques Delors Professor of European Law at Oxford University. “In the absence of any provision, there is plenty of space for European governments to concoct a solution, adopt it and for it to be legally enforceable,” he added. “In general, you can do anything you like, so long as you do not breach pre-existing international obligations.” The mechanics of leaving the euro would surely lead Greece to impose so-called capital controls to stem the flight of money from a currency destined to be devalued. Again, such controls look impossible under E.U. law. But Mr. Weatherill thinks that a loophole allowing for the protection of public security could be invoked. Mr. Clark, of White & Case, a global law firm, points to a clause in Article 65 of the treaty that says that the pledge on free movement should not prevent countries from taking measures “which are justified on grounds of public policy or public security.” Mr. Clark and his team serve clients that include financial institutions like BNP Paribas and hedge funds. In February, Andrew Witty, the chief executive of GlaxoSmithKline, said: “We don’t leave any cash in most European countries” except Germany. Tens of millions of pounds flow into accounts in Britain every day, he said. But, apart from trying to ensure that debts are paid promptly and therefore in euros, legal options for companies are limited. Contracts covered by Greek law, particularly for services delivered in Greece, provide little protection against the currency’s being redenominated and devalued — a development regarded as unlikely until recently. “Greece would, through its laws, be able to amend contracts governed by Greek law or to be performed within the territory of Greece,” Mr. Clark said. “It is the governing law and the place of performance of the contract that is most important.” International contracts, which might be covered by English, German or Swiss law, would be more likely to be honored in the designated currency, though in some cases the wording of the legal document may be vague. And even if the law is on their side, companies would find that to extract payment from a Greek company, they would need a judge in Greece to enforce a ruling from a foreign court. “Enforcement of foreign judgments is harder or easier from country to country within the E.U.,” Mr. Clark said. “Greece has always had a reputation of being a difficult place in which to enforce judgments, from a practical perspective.” That means that international trading partners are likely to share in any losses that accompany a Greek exit from the euro. “International businesses that have long-term interests in Greece are going to have to be pragmatic and probably, in the short term, give some dispensation to their Greek counterparties, rather than trying to enforce the terms of contracts that cannot be performed,” Mr. Clark said.

A former head of security at Lloyds Bank has been charged in connection with an alleged £2.5m fraud. Jessica Harper, 50, of Croydon, south London, is accused of submitting false invoices to claim payments, between September 2008 and December 2011. At the time she was working as head of fraud and security for digital banking and allegedly made false claims totalling £2,463,750. Ms Harper will appear at Westminster Magistrates' Court on 31 May. She has been charged with one count of fraud by abuse of position. The bank, which is now 39.7% state-owned after being bailed out by the government during the financial crisis, refused to comment on the charging of Ms Harper. A Metropolitan Police spokesman said she was arrested on 21 December 2011 by officers from its fraud squad. Andrew Penhale, from the Crown Prosecution Service's Central Fraud Group, said: "The charge relates to an allegation that between 1 September 2008 and 21 December 2011, Jessica Harper dishonestly and with the intention of making a gain for herself, abused her position as an employee of Lloyds Banking Group, in which she was expected to safeguard the financial interests of Lloyds Banking Group, by submitting false invoices to claim payments totalling £2,463,750.88, to which she was not entitled. "This decision to prosecute was taken in accordance with the Code for Crown Prosecutors. "We have determined that there is a realistic prospect of conviction and a prosecution is in the public interest."