Symantec is advising users of its pcAnywhere remote access product to disable the software if they don't absolutely need it.
The company this month confirmed that hackers stole a portion of its source code dating back to 2006.
The code related to the 2006 versions of Norton Antivirus Corporate Edition, Norton Internet Security, Norton SystemWorks and pcAnywhere.
Symantec said that the code was old enough that users of the Norton products would not face any increased threat of attack, the note said.
But pcAnywhere customers were "at increased risk", it said, in contradiction to its earlier statements that its products were not vulnerable due to the theft and that its own network was not breached.
"Our current analysis shows that all pcAnywhere 12.0, 12.1 and 12.5 customers are at increased risk, as well as customers using prior versions of the product," Symantec said this week.
"PcAnywhere is also bundled with numerous Symantec products. The full standalone product is bundled in a number of Altiris-based solutions."
Altiris products perform IT management functions.
A whitepaper released Wednesday recommended that pcAnywhere users stop using the software until permanent patches are available, unless they require it for mission-critical operations.
"Malicious users with access to the source code have an increased ability to identify vulnerabilities and build new exploits," the paper said.
"Additionally, customers that are not following general security best practices are susceptible to man-in-the-middle attacks which can reveal authentication and session information.
"At this time, Symantec recommends disabling the product until Symantec releases a final set of software updates that resolve currently known vulnerability risks."
In a Wednesday security advisory, Symantec disclosed two vulnerabilities, one related "high" in severity, that impact pcAnywhere.
The flaws can be exploited to elevate privileges or execute remote code, and Symantec has made available a hotfix.
In addition, the company issued recommendations for organisations that require the use of remote access software, such as pcAnywhere. They include setting corporate firewalls to bar inbound or outbound traffic not using VPN tunnels, and creating password-strength policies.