Virus writers are increasingly targeting more recent security vulnerabilities in their attempts to spread malicious code.

The latest bi-annual Internet Security Threat Report from Symantec found that 64 per cent of all new attacks targeted vulnerabilities less than one year old. The Blaster worm, for example, appeared only 26 days after the vulnerability it exploited was announced.

Some 66 per cent of all attacks documented in the first half of 2003 exploited vulnerabilities categorised as highly severe.

Symantec's study paints a picture of a rise in more sophisticated and faster spreading worms, and the increased use by virus writers of new vectors for infection (such as P2P networks and IM applications).

Symantec reports that the increasing prevalence of blended threats, which use a combination of malicious code and vulnerabilities to launch a cyber attack, remains one of the most significant security issues companies face this year. Blended threats accounted for 60 per cent of malicious code submissions in the first half of 2003, and the number of blended threats increased by 20 per cent.

Looking ahead, Symantec expects to see greater worm propagation resulting in overloads to network hardware, crippling network traffic, and seriously preventing both individuals and businesses from using the Internet. A gloomy forecast then.

Symantec's report includes analysis of data from Symantec Managed Security Services customers as well as information obtained from the firm's firewall and IDS users. The report covers network-based attacks, a review of vulnerabilities discovered and exploited, and highlights of malicious code trends.

Key attack and vulnerability trends picked up by the survey include:

• The overall rate of attack activity rose by 19 per cent. Companies experienced approximately 38 attacks per company per week in the first half of 2003 compared to 32 attacks during the same period in 2002.
  
• Attacks are increasingly leveraging worms to carry exploits of known vulnerabilities as a means of creating exposures or security holes on a large number of systems. Attackers are then installing backdoor Trojans on those compromised systems to create large networks of controlled systems (zombie nets) that could be used to launch future attacks. Submissions of malicious code with backdoors to Symantec rose from 11 in 1H2002 to 17 in 1H2003.
  
• Symantec documented 1,432 new vulnerabilities, a 12 per cent increase over the number found in the same period the previous year. However, the rate of discovery during the first half of 2003 was significantly slower than the 82 per cent increase noted in 2002. More than 994 new Windows viruses and worms were documented in the first half of 2003, more than double the 445 documented in the first half of 2002.
  
• Worryingly, Symantec reports that 70 per cent of the vulnerabilities found in the first half of 2003 could be easily exploited, due to the fact that no exploit was required or an exploit was readily available. This represents an increase of 10 per cent over vulnerabilities discovered during the first half of 2002.
  
• Virus writers are increasingly leveraging instant message and P2P networks as a means of spreading malicious code. Of the top 50 malicious code submissions documented over the first half of 2003, 19 used peer-to-peer and instant messaging applications - a fivefold increase over the course of only a year.

Symantec encourages users and administrators to adhere to the following best security practices:

• Turn off and remove unneeded services.
  
• Keep patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  
• Enforce a password policy.
  
• Configure email servers to block or remove email that contains file attachments commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
  
• Isolate infected computers quickly, perform a forensic analysis and restore computers using trusted media.
  
• Train employees not to open attachments unless they are expecting them (D'oh). ®

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