Amid steep cash inflows, Munder Funds today announced plans to close its ( MNNAX) NetNet fund to new investors April 17. After that, only current shareholders will still be able to buy shares of the largest Internet-focused fund.

The $11.5 billion broker-sold fund is larger than all other Net funds combined. It's closing to keep its size from impeding its ability to invest effectively in the subsector. At the end of last month, the fund's cash stake was a modest 4.1%, but the closing strategy is curious. Typically when a fund closes, it sets an asset limit or gives just one or two days' notice. Fund-watchers have often said that hot fund closings announced weeks in advance like this one trigger a "limited-time offer" buzz, ironically or intentionally leading to a mountain of cash.

Investors have been stuffing money into tech funds at a record pace over the past year, and NetNet has gotten more than most. The fund started 1999 with less than $1 billion and finished the year at $7.4 billion. It was the 14th top-selling fund last year with inflows of $3.7 billion, according to Boston fund consultant Financial Research, and it took in another $604 million in January.

As usual, all of those checks came on the heels of hot performance. Started in August 1996, the fund has ridden one of the hottest sectors of the market. NetNet's stunning 121% three-year annualized return, though outshined by the ( WWWFX) Internet fund's 147%, beats nearly every technology fund and thumps the S&P 500 by more than 95 percentage points, according to Morningstar.

The cash gushing into the fund might be slowing it down -- albeit slowly. The fund's 143% return over the past year actually trails 72% of its tech fund peers, according to Morningstar. Its 29% return since Jan. 1 matches its category average.

Media darling Paul Cook leads the fund's five-member management team. He's known for a somewhat diversified investment approach, stretching the definition of a Net company to include broader tech plays like Cisco ( CSCO), Oracle ( ORCL), and Sun Microsystems ( SUNW). It does, however, have a healthy dose of "pure play" exposure like InfoSpace.com ( INSP), the fund's top holding on Feb. 29, which is up more than 60% this year.

Like the Net sector, the fund's performance has come in gaudy bursts. It returned more than 175% last year, almost 80% in the fourth quarter alone. It has also posted losses in four of 13 quarters since its inception, the worst being a 21.2% downturn in 1997's first quarter.

Munder has prepared for its top-seller's closing by developing other tech funds run by members of NetNet's management team. Last October, the firm launched ( MTFAX) Future Technology , and it will launch International NetNet April 3.

Future Technology is up 42% since Jan. 1 and already has more than $2 billion in assets.

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