A week ago Compete released search engine rank numbers that showed Microsoft making a huge jump in usage. To be more precise, Compete said usage of Microsoft search properties (MSN/Live.com) surged 67% for the month of June.

As usual, I held off making any wild assumptions based on one set of data. But comScore has released their market share numbers for June and are showing a similar - although significantly smaller - increase in Microsoft traffic:

Microsoft Sites experienced a significant increase in search query volume (up 36 percent) and search market share (up 2.9 share points) in June, due in large part to Live Search Club, a program launched by Microsoft in late May to engage and reward users of Live Search.

Although the boost in traffic is almost half as much as Compete is reporting, the trend is nevertheless the same. In fact, according to comScore, Microsoft was the only search company to see an increase in month-to-month traffic. All other search engines either saw stagnant or declining usage stats.

So is this Live Search Club the only reason the numbers are up? After publishing their initial numbers, Compete re-ran their stats and eliminated all traffic from Live Search Club. The results were less dramatic… but MSN/Live.com still showed a marked increase in usage for the month.

As we’ve said before, this isn’t really that surprising. Live Search Club aside, Windows Vista and Internet Explorer are both driving users to MSN/Live.com. As Vista adoption continues to increase, so too should Microsoft’s search numbers… in theory.

As I’ve said before… the “in theory” part applies here because Microsoft has yet to prove it can keep customers once they arrive. If as many (or more) people are ditching MSN/Live.com search after being sent there by IE7 or Windows Vista, these increases in usage mean nothing.

But if Microsoft can hold on to even a fraction of that traffic… it could mean trouble for Yahoo.