Munich  - It all used to be simpler for Mac users: viruses and other malicious software affected Windows computers, not them. That is slowly changing. "The threats have intensified," says Candid Wuest from anti-virus maker Symantec.

The biggest threat comes from hackers trying to sneak viruses onto computers. OSX. RSPlug. A is the name of one that preys on Mac users. It claims to be a video codec required to watch certain porno films, but in fact tries to redirect the surfer to a website forged to look like an eBay page. An attempt is then made to phish for the access data to the user's real eBay account.

"This trojan hasn't drawn much attention," says Walter Mehl from Germany's Macwelt magazine. That may have to do with the fact that it is spread only through porn sites. It was also shoddily programmed.

Another trojan assumed control of Macs earlier this year, harnessing them into a "Botnet," Wuest says. A botnet is a remote controlled network of computers employed by hackers to send out spam. Some 10,000 to 20,000 computers have been infected to date. That number, however, pales in comparison with the countless Windows PCs infected by the Conficker worm.

Windows is a more common target for attacks partially because it's the user base is much larger. Virus writers know that with so many more computers running the software, even viruses that infect only a fraction of their targets can still rack up big numbers. The same is true for the search for vulnerabilities in applications - common programs are a favourite target.

Malicious software used to be written only for specific operating systems. That has changed to some extent, Mehl says. For example, it was recently discovered that rigged PDFs could exploit a security hole in Adobe Flash, a popular software component. The problem affects both Windows and Mac OS (Operating System) machines. Users are advised to keep not just the operating system and virus scanners current, but also programs like Flash or Firefox.

"There is still less malware for the Mac," Mehl says. Yet more and more people are working with the Mac OS and turning up vulnerabilities that have not yet been exploited. The threat potential has grown. "That's why I feel that protection software is now important on Mac OS as well," says Mehl.

Apple claims that the Mac uses integrated technology to fight off malware. Yet since no system is 100 per cent immune from attacks, anti-virus software provides a supplemental layer of protection. Macwelt magazine sees two usable security programs for Mac OS: Norton Internet Security for Mac from Symantec and VirusBarrier from Intego.

Installing anti-virus software is just part of the battle, Candid Wuest says. "No matter which OS you use, you need to be constantly mindful." Phishing attacks, where criminals try to trick users into divulging passwords or other data, affect Mac users just as much as Windows or Linux users. That means that users should think twice before clicking unsolicited links - be it via e-mail, Twitter, or any other delivery method the internet can provide. (dpa)