Windows 8 is prone to infection according to controlled tests from security software company Bitdefender.

The newly launched operating system is alleged to be open to 15% of the 100 malware families most used by cyber criminals this year, even with Windows Defender activated.

Bitdefender says the software was infected by 61 malware threats of 385 of the most popular samples in a tests carried by leading virus researchers over the past week.

Other samples bypassed Windows Defender but crashed on execution, while one ran but was blocked by User Account Control, so no payload was delivered.

“As a means of protecting a computer from viruses, data theft and other type of malware, Windows Defender is better than nothing,” says Catalin Cosoi, Bitdefender chief security strategist.

“But it’s not a whole lot better. Most of the popular antivirus can do better.

"The conclusion is clear: Using your PC without a security solution is extremely risky.”

The malicious sample set consisted of the families of malware detected most frequently in the past six months by the Bitdefender Real-Time Virus Reporting System.

After successfully bypassing Windows Defender, the company says the malware was capable of granting backdoor access to the system, intercepting keystrokes and stealing online games credentials.

When tested without Windows Defender activated, the results were worse however, with 234 running successfully out of the 385 tested.

Another 138 samples could not be started on the machine for various reasons according to the report, with six e-threats executing but then crashing, and seven others launching but had their payload was blocked by UAC.

“Even if the new operating system boasts a major overhaul in terms of visuals with the introduction of the Advanced UI, Windows 8 with the default antivirus solution activated registers alarming detections rates similar to the one registered by Windows 7,” says Alexandru Balan, Bitdefender chief security researcher.