JACKSONVILLE, Fla. -- Rail traffic throughout the Southeast was slowly returning to normal Wednesday afternoon after a computer virus disrupted CSX's telecommunications network which some systems use to control signaling, dispatching and other systems.

As a result, passenger and freight train traffic was halted immediately, including the morning commuter train service in metropolitan Washington, D.C.

The Jacksonville-based rail line said the cause was believed to be a worm virus similar to those that have infected the systems of other major companies and agencies in recent days.

The signaling system went down about 1:15 a.m. and briefly affected the entire CSX system, which covers 23 states east of the Mississippi River.

WHAT IS IT? How Viruses, Worms Work VIRUS PROTECTION Virus removal tool | Netsky removal Microsoft patch GENERAL PROTECTION Sign Up For Cyber Alerts Download Virus Definitions Other Virus Removal Tools Securities Update Vault REMEMBER: Don't open e-mail attachments that end in .vbs, .pif or other unfamiliar extensions. Even if the e-mail appears to come from a trusted source, it could be someone "spoofing" an address. Confirm it's from who you think it's from before you open.

Although the problem was largely corrected by midday, there were some residual problems that caused delays of up to six hours to Amtrak service in the mid-Atlantic region, Amtrak spokesman Dan Stessel said.

"Most of the delays are in the 15- to 30-minute range on trains that travel through CSX territory," Stessel said.

Ten Amtrak trains were affected, Stessel said. Trains between Pittsburgh and Florence, S.C. were halted because of dark signals and one regional Amtrak train from Richmond, Va., to Washington and New York was delayed for more than two hours.

Long distance trains were delayed between four and six hours.

"When CSX bought out all those other railroads, they put the signaling all together down in Jacksonville, Florida," one D.C. area passenger said. "It simply doesn't work."

Several local commuter rail lines in Maryland, West Virginia and suburban Washington D.C. were affected, making the morning commute difficult.

CSX told Channel 4's Adam Landau that its computers were mostly repaired by 7:30 a.m., but it could take 24 hours for the rail system to completely recover.

Passengers with questions about service and schedules and delays should contact Amtrak directly.

SURVEY How is the SoBig.F virus affecting you? My inbox is hopelessly flooded. My filters are making it easier. I've seen a few odd messages. It's not affecting me at all. Results  |  Disclaimer

It was unclear if this was the same virus that flooded computer networks and inboxes Tuesday and Wednesday.

Computer security experts warned Wednesday that the SoBig.F virus that started replicating itself will get worse before it gets better.

"We have not seen the peak as of yet," said Scott Chasin, chief technology officer of MX Logic, a company that sells e-mail defenses. News4Jax.com is a client of MX Logic.

Chasin said 30 percent of the company's clients have been attacked, but the number of victims is growing. As of noon, Central time, Wednesday, MX Logic had blocked 4 million attacks, and that number is "growing by the minute."

Previous versions of the virus, as well as others such as the Klez virus, sent messages one at a time from a single, faked e-mail address. The new type take an address from the infected computer's address book, and use that as the "from" line, making it appear more like legitimate mail. It can also send to hundreds of addresses at once.

This can result in returned-mail messages for users who don't have the virus. If someone you know gets infected, his or her computer could "spoof" your name onto the copies of the virus that are sent out. If they reach invalid addresses, or are blocked by a virus detector that sends a warning to the supposed sender, the notification would return to your inbox.

Subject lines associated with the new SoBig.F virus include "Thank You!" "Your details," "Details," "Wicked screensaver," "Resume," "Approved," and "That movie." If your e-mail program allows you to set rules or filters for your inbox, funneling messages with those subject lines to your deleted items could save you some time.

In popular e-mail clients such as Microsoft Outlook and Outlook Express, go to the Tools menu to set up the rules. In Outlook, look for the "Rules Wizard. In Express, look for "Message rules." You can elect to have messages with the above subject lines automatically deleted, or you can create a special folder the program diverts the mail to. That way, you can review the messages to make sure nothing legitimate is deleted.

People whose addresses are available on the World Wide Web, or those who are on distribution lists that are available, can see high volumes of returned mail. Those addresses are often used because they are in many contact lists, since popular programs like Outlook Express automatically save e-mail addresses.

Editors for Internet Broadcasting Systems, which hosts News4Jax.com, found that instead of the usual hundreds of e-mails arriving in their boxes, they were receiving thousands. One said that he received an average of almost 1.5 e-mails every minute during the overnight hours Tuesday.

The company itself, though it did not appear to have any infected computers, received five times the normal amount of e-mail over a 24-hour period Tuesday and Wednesday, and network administrators said they could not guess when the flow might slow.