Attacks by malicious programs - which include often invisible threats such as worms and Trojan horses - jumped over 40 per cent in the first half of this year, according to the report, released earlier this month.

Many of the viruses are designed to mine personal computers for data ranging from your home address to your online banking password. Others can take over your computer, which hackers use to carry out other attacks, shielding their identities from law-enforcement agencies.

Personal data can be worth a small fortune in the underground economy; hackers bought and sold US$276 million (S$422 million) worth of such data from July last year to June, said a report yesterday by security company Symantec.

The attacks are getting more serious and more numerous as the hacker profile moves away from the pimply teenager seeking online fame to organised crime syndicates looking for new revenue streams, experts said.

Microsoft platform strategy manager Matthew Hardman said social networking sites, like Facebook, are among the most commonly targeted because of their huge communities of users.

He said malicious code may be hidden inside Facebook applications or in links under photographs.

In Singapore, where about 75 per cent of all households are connected to the Internet, 10 per cent of Web surfers use their connection primarily for social networking. Twelve per cent use it for interactive online games, which are another frequent target of hackers.

Symantec's regional consumer product marketing manager for the Asia-Pacific, Mr David Hall, said: 'We have never done so much online or shared so much online. So the attackers are just going where there's money to be made.'

Security firm Sophos' Asia-Pacific head of technology, Mr Paul Ducklin, said that social networks are still in a 'honeymoon' phase. 'So we tend to have a blind spot and are careless.'

Experts say Internet users can keep safe by being circumspect about sharing personal information, and making sure their computers have up-to-date anti-virus programs.

'Having a lock on the door doesn't protect your gold,' said Mr Hardman. 'You have to lock the door yourself.'

serl@sph.com.sg