It's shaping up to be a bad week for antivirus software company Symantec after researchers raised alarms about security holes and buggy code in two of the company's products. It's shaping up to be a bad week for antivirus software company\u00a0Symantec\u00a0after researchers raised alarms about security holes and buggy code in two of the company's products.On Monday, Symantec acknowledged a report about a serious security flaw in Symantec Security Check, a free online service that enables users to scan their computer's vulnerability to a number of security threats.According to a message posted in the online discussion group Full-Disclosure on Sunday, an ActiveX control installed by the Security Check service contains a buffer overflow vulnerability that could enable a remote attacker to crash or run malicious code on systems that had the control installed.The control, named "Symantec RuFSI Utility Class" or "Symantec RuFSI Registry Information Class," is used to run the security check, but remains on systems after the scan is complete, according to a statement from Symantec.After learning of the security hole on Monday, Symantec updated the ActiveX control in the Security Check service. Individuals that re-scanned their systems would receive the updated control.Symantec also provided instructions on updating the control or removing it from affected systems.However, security researchers monitoring the issue noted that simply updating the control still left users vulnerable to attack, especially if that control contains Symantec's digital signature.Attackers who have a copy of the flawed ActiveX code with a valid digital signature could trick Microsoft\u00a0Windows systems into accepting the control, opening that system to attack even if it did not already have the faulty component installed, according to a notice posted to Full-Disclosure by Jason Coombs, a software security expert in Kea'au, Hawaii.Symantec acknowledged that the new control uses the same digital signature as the flawed one and is "looking into" that issue, according to Anson Lee, product manager for Norton Internet Security at Symantec.In the meantime, the company is encouraging Internet users to apply so-called "best practices" when prompted to download an ActiveX control.Best practices include scrutinizing the signature of ActiveX components before agreeing to download them, Lee said.Users should be suspicious when third party Web sites ask you to download an ActiveX component signed by Symantec, according to Vincent Weafer, senior director of Symantec Security Response.In the meantime, the flawed ActiveX control from the Security Check service could be an attractive target for hackers.Symantec estimates that more than 30 million individuals visited the Symantec Security Check site since its inception, Lee said.The company does not know how many of those users actually scanned their system, nor does it have any way to contact users who did, he said.Symantec is in the process of creating a tool to help remove the ActiveX control from affected machines. A team at the company is also investigating ways to nullify the faulty control, but could not comment on any progress in that search, Lee said.Symantec also found itself in hot water on Monday after customers using Symantec AntiVirus Corporate Edition reported that an automated antivirus definition update from the\u00a0security company caused the antivirus software to fail. The problem was disclosed in the NTBugtraq discussion list on Monday.The problem stemmed from a faulty antivirus "microdefinition update" distributed on June 19, according to Russ Cooper, NTBugtraq moderator and surgeon general of TruSecure.Microdefinition updates are a new feature with Version 8 of the Symantec AntiVirus Corporate Edition that enable systems running the software to download small, incremental antivirus definition updates rather than large, comprehensive definition update files, Cooper said.Symantec's antivirus software would not start on desktop systems that installed the faulty update, leaving some customers without antivirus protection on desktops and servers running the software.The flaw affected a Symantec antivirus service called the "realtime scanner" that runs in the background while users work and monitors files and other resources for viruses, according to Weafer.A second service, the "on-demand" scanner was not affected by the problem, he said.Cooper received confirmation of the problem from at least 30 companies. "Thousands" of systems running the software were affected, he said.Symantec put the number of affected customers at fewer than 40 worldwide, according to Vincent Weafer."It's a very focused group of people using a special type of deployment," he said.A Symantec knowledge base document created June 20 and updated on Monday acknowledged the existence of the faulty update and provided instructions on repairing systems that downloaded the faulty update.Customers affected by the bad antivirus update should remove it from "parent" distribution servers and desktops on their network before obtaining and loading the valid definition update file on the distribution servers, which will then distribute the file to affected desktops.Downloading and deploying a full antivirus definition update would "flush" the flawed incremental update from systems on which it was installed. Symantec also released a tool to help administrators automatically restart the realtime scanner on systems affected by the vulnerability, Weafer said.Antivirus Corporate Edition version 8 systems that downloaded a full definition update (.vdb) file or that acquired virus updates using Symantec's LiveUpdate or Intelligent Updater services are not affected, Symantec said.The company has not received reports of more customers affected by the problem, but is still working with some customers to refresh machines affected by the bad definition update and restart services on those machines, Weafer said.The problems are just the latest examples of problems introduced by antivirus companies.In May, Trend Micro\u00a0was\u00a0forced to issue a fix\u00a0for an embarrassing snafu caused by an update to the eManager e-mail security product that blocked all e-mail containing the letter 'P.'The problem stems from popular "auto-update" features that automatically distribute virus definitions and software updates to remote systems, Cooper said.Such mechanisms frequently lack features to verify that such updates are properly installed on the systems that receive them, or to roll back faulty updates in the event that problems are introduced, he said.Antivirus companies also frequently use the update features to silently distribute software patches to their customers, Cooper said.As currently implemented, such systems can easily and quickly distribute buggy or vulnerable code to thousands of systems, he said."Here we have Symantec attacking their own customers with a flaw. So we don't have to worry about the bad guys doing it. Symantec is doing it for them," Cooper said.