Microsoft is disputing reports of new three flaws in its Office software while also taking issue in how the alleged flaws were disclosed.

Several security websites reported four new vulnerabilities, three affecting Word 2007, just as Microsoft released its latest round of security patches this week.

Microsoft said none of the three alleged to affect Word 2007, "demonstrate any vulnerability in Word 2007 or any Office 2007 products".

The company also said it was not notified of the alleged problems before they were publicly disclosed, a practice generally frowned upon in the security industry.

At least two of the websites have in the past posted exploit code prior to notifying vendors, said Graham Cluley, senior technology consultant at security vendor Sophos.

Two of alleged Word 2007 problems are said to cause central processing unit (CPU) usage to surge to 100%, creating a denial-of-service condition, according to a posting on the Security Vulnerabilities website. The third vulnerability, also concerning Word 2007, could supposedly allow remote code execution.

The fourth alleged vulnerability, which concerns the ".hlp" extension for Windows help files, could lead to a heap overflow condition, the site said. Microsoft acknowledged the problem, saying that .hlp is an "unsafe file format" and is executable, meaning that it will run code when opened.

The company said users should be cautious about opening unsolicited e-mail attachments with .hlp files.

Microsoft issued seven fixes for critical flaws on Tuesday. Hackers have often timed the disclosure of new vulnerabilities just after Microsoft's patch day, the second Tuesday of the month, to maximise their time to exploit computers, said Greg Day, a security analyst for McAfee. "It's becoming a very common trend," he said.

Security researchers have also said that as Microsoft fixes problems within its operating systems, hackers are actively hunting for flaws in its Office applications.

When they find one, hackers will send spam with, for example, a malicious Word document attached. Downloading and opening the file could allow a hacker to take control of the machine. Microsoft has warned that people should not open files sent from unknown sources.

April is proving to be a rough month for Microsoft: It issued an emergency patch on 3 April for an animated cursor flaw, which could let a hacker control a machine after its user merely views a malicious website.