Local internet service providers have been flooded with incoming e-mails after the computer worm MyDoom was unleashed last week.

MyDoom.A, also known as Novarg, was sent out to e-mail boxes on Monday and a variant, MyDoom.B, was created on Thursday.

The worms are similar in that they are mass-mailing error messages and arrive in the form of an attachment.

The worm is activated if the attachment is clicked on.

Computer security provider, QuoVadis, said 25 percent of incoming e-mails were carrying MyDoom on Friday.

But anti-virus companies have marked MyDoom.B?s risk as low but MyDoom.A has been labelled as ?severe? because it has been difficult to contain.

Because the containment has been so difficult and variants can pop up at any time, Logic Communications marketing manager Karla de Sousa advised computer owners to update their anti-virus protection daily.

She said the worm and its variant is causing a ?strong surplus of traffic? but she added that even a small network like Logic has been able to keep up with the overflow.

When the worm was first let loose, Logic?s server was knocked down for a few hours.

?The sheer volume of mail has dramatically increased but we?re still able to process everything the same in real time.?

Stephen Davidson, vice president of product development at QuoVadis, explained that the added volume of incoming mail can be contributed to return e-mails that many servers send if they have received an infected message.

?Many companies are suffering, even if they have solid anti-virus protection, from the flood of incoming messages. The e-mail servers must handle it all, good or bad. That?s one of the reasons that our customers have been using Sweeper. We act as the first line of defence and filter out the unwanted spam and infected e-mails,? he said.

Yesterday, MyDoom.A launched a Denial of Service attack on SCO Group Inc., the software solutions company that produces UNIX operating systems and crashed SCO?s server.

The attacks aim to send ?malformed? requests to a certain Internet server and once so many requests are launched it can cause the server to die, Mr. Davidson explained.

MyDoom.B was set to launch the same attack on Microsoft Corp. but as of yesterday the company was able to avoid the attacks. Few other servers were experiencing failed requests yesterday.

?There are ways to evade this attack,? Mr. Davidson said. ?This happens to companies so many times.?

Both SCO and Microsoft have offered an award of $250,000 for information to lead to the arrest of the creators of the worm and its variant.