The Netsky-P and Zafi-B worms are running neck and neck for the top spot in June's list of Worst Malware Threats.

While Sophos, Inc., a Lynnfield, Ma.-based anti-virus and anti-spam company, ranks Zafi-B as the most prolific threat last month, Central Command, Inc., a Medina, Ohio-based anti-virus company, puts Netsky-P at the top of their June list.

According to Sophos, Zafi-B accounted for 30.4 percent of all malware traveling the Internet last month, and Netsky-P came in with 9.9 percent. But Central Command, showed pretty much opposite results with Netsky-P accounting for 32.7 percent of malware and Zafi-B making up 8.8 percent.

''Statistics are collected differently, but these are two bad worms that we've been dealing with,'' says Carol Theriault, a security consultant with Sophos. ''The Netsky family, in particular, has caused a lot of trouble for us this year. There are more than 30 variants. The guy claiming ownership of them has been arrested in Germany so hopefully we won't see any more of these. But they've been around since January and we're still seeing them in our top 10.''

Theriault says Zafi-B has caused a large number of infections in Eastern Europe. The text message in the Zafi-B email is written in Hungarian and is rather old-school in that it carries a political message (new worms are more focused on financial gain than in railing against Microsoft or the government).

And many users in the United States were infected with Zafi-B because their anti-virus software couldn't read the Hungarian text so the virus slipped through the protective layer.

What Central Command and Sophos do agree on is that June was a quieter month than the several months that preceded it.

''Unlike earlier this year, June was relatively tranquil,'' says Steve Sundermeier, a vice president at Central Command.

Theriault says Sophos had added 900 new virus identities to its anti-virus software in May, but that number dropped to 670 this past month. ''Normally, we see between 600 and 800 a month,'' she adds. ''June was more average again.''