Vulnerabilities were discovered in MSN Messenger 7.0, due to be released today, after testers found it had the potential to send rogue 'winks' – animations that grab the reader's attention.
"The Messenger beta was designed to only send approved MSN winks," said a spokesperson for Microsoft. "That said, we're investigating the potential that hackers could bypass this process to send unauthorised -- rogue -- winks that could cause security issues. We will not ship winks with the limited beta so we can address any potential issues."
The company did not mention what the potential issues were.
Microsoft is set to release a beta version next week in the US, UK and some parts of Europe, but will exclude the winks feature while it researches the problem.
The company said it was committed to delivering a secure product and would not make a public release until all the issues had been addressed.