Onel de Guzman, 23, who had been missing for several days, appeared at a news conference in dark glasses.

The bug could cause up to $10bn damage

He did not directly say whether he had written the "ILOVEYOU" virus, and said he was unsure whether he had released it into cyberspace.

"He is not really aware that the act imputed to him was done by him," his lawyer said.

When asked whether he might have accidentally released the virus, Mr de Guzman replied: "It is possible".

He said he did not remember where he was on 4 May, the day Love Bug erupted. Asked how he felt about the damage caused by the virus, he replied: "Nothing".

Thesis

The virus, which spread via an e-mail bearing the line "ILOVEYOU", is believed to have affected at least 45 million computer users and caused billions of dollars of damage.

Earlier this year Mr de Guzman, a former student at Manila's AMA Computer College, wrote a thesis project describing an e-mail stealing program similar to the Love Bug.

De Guzman dropped out of school

He failed to graduate after the school rejected his paper as unethical, saying it did not condone "burglary".

Investigators believe they have traced the source of the virus to a computer at the apartment owned by Mr de Guzman's sister Irene.

The authorities have summoned both to appear before investigators on Thursday.

Ms de Guzman's live-in boyfriend Reonel Ramones was arrested on Monday following a raid on their home. He was released the following day pending further investigations.

Theft

AMA Computer College said Mr de Guzman had excelled in his computer courses, but dropped out after his thesis proposal was rejected.

Tackling the virus

Do not open it Delete it using shift del As with all e-mails, if in doubt do not run any attachments you are not expecting If you have run the attachment, isolate your machine from any network and phone your help desk or seek expert advice Remember to keep your anti-virus software up-to-date and be vigilant about attachments

In his paper, Mr de Guzman said his software would help users obtain Windows passwords and spend more time on the internet without paying.

"We spend a lots of money to pay [for internet] accounts for only using a couple of hours," he wrote.

"So this program is the main solution. Use it to steal and retrieve internet accounts of the victim's computer," he added.

The former student said he had discussed his thesis with other people.

Asked whether Mr de Guzman was responsible for the virus, his lawyer replied: "We can go as far as saying that he did prepare the thesis proposal but ... the knowledge of its contents was not limited to Onel".

Underground group

Reports say college officials from AMA are also focussing attention on another student, Michael Buen, a close friend of Mr de Guzman's.

Both are members of GRAMMERSoft, an underground computer group that wrote and sold thesis projects to other students, according to the Associated Press news agency.

The name GRAMMERSoft reportedly appears in the computer code in the Love Bug virus.

FBI officials, who are helping in the investigation, have found 10 coded names embedded in the virus. But the names could be pseudonyms of a single person or just a few people.

The Love Bug virus only affects systems running Microsoft Windows with Windows Scripting Host enabled. Computers using Apple's operating system or Linux are not affected.