The latest worm exploits security holes in Microsoft's Windows 95, 98, ME, NE, 2000 and XP platforms and can give computer attackers remote access to affected systems, said Trend Micro Inc.
"Hundreds of infection reports were sighted in the United States and Germany," Tokyo-based Trend Micro said in a statement released late last week.
"Since most users may not be aware of this newly announced security hole so as to install the necessary patch during last weekend, we can foresee more infections from WORM_ZOTOB," it said.
The latest virus drops a copy of itself into the Windows system folder as BOTZOR.EXE and modifies the system's host file in the infected user's computer to prevent the user getting online assistance from antivirus web sites, Trend Micro added.
It can also connect to a specific Internet relay chat server and give hackers remote control over affected systems, which can be used to infect other unpatched machines in a network and slow down the network performance.
Last Tuesday, Microsoft issued patches to fix its security flaws as part of its monthly security bulletin. The problems affect the Windows operating system and Microsoft's Internet Explorer Web browser.
Microsoft has warned that an attacker could exploit a vulnerability in its Internet Explorer Web browser and lure users to malicious Web pages, and could run a software code on the user's PC giving the attacker control of the affected computer.
Computer users should update their anti-virus pattern files and apply the latest Microsoft patches to protect their computer systems, Trend Micro said.
More than 90 percent of the world's PCs run on the Windows operating system and Microsoft has been working to improve the security and reliability of its software.