Another day, another record intraday high for the broad-based S&P 500 which continues to be unstoppable since its mini-April swoon.

Although no economic data helped lead the S&P 500 to a fresh all-time intraday high near 1,956, a number of merger and acquisition events and rumors – which we'll get to in a moment -- wound up fueling interest in stocks and pushing them to the upside once again. M&A activity is an important indicator for investors as it signals that purchasing companies are willing to take on risks and pay a premium for a rival, presumably because it sees growth ahead and has moderate-to-good long-term visibility.

Meat products producer Hillshire Brands, for example, incited a bidding war that led to a total of four bids with Tyson Foods coming out the victor with a $63-per-share bid. That's pretty impressive considering the initial offer from Pilgrim's Pride was a mere $45 per share two weeks ago.

Taking in today's M&A activity the S&P 500 wound up trudging its way higher by 1.83 points (0.09%) to close at 1,951.27, its ninth record closing high in just the past 11 sessions.

Leading the charge higher for individual stocks, by a long shot, was hepatitis C-focused Idenix Pharmaceuticals (UNKNOWN:IDIX.DL) which skyrocketed 229.1% (no I didn't misplace a decimal point – that's really 229.1%!) after agreeing to be purchased by Merck (NYSE:MRK) for $3.85 billion, or $24.50 per share in cash. The deal represents a 239% premium to Friday's closing price and will allow Merck access to Idenix's nucleotide/nucleoside and prodrug technologies platform which it believes will complement its own existing hepatitis C therapies in development.

Source: University of Michigan Medical School Information Services, Flickr.

Personally, though, I called this among the worst deals I'd ever witnessed earlier today. Consider for a moment that since 2010 Idenix has had four of its then leading clinical drugs placed on clinical hold by the Food and Drug Administration. Of those four, three were eventually discontinued, with one actually being placed on hold twice (IDX184). With the company having been unsuccessful at getting any of its investigational drugs into late-stage studies the thought of paying $3.85 billion in cash is ludicrous in my opinion. It's possible Idenix's samatasvir, its lead NS5A inhibitor, could prove successful, but Idenix is already so far behind its peers in the development process that I have to wonder if it'll even be worth it! Long story short, I believe this to be a bad move for Merck over the long run.

Source: ZEISS Microscopy, Flickr.

Following suit, Achillion Pharmaceuticals (NASDAQ:ACHN), another hepatitis C focused drug developer, shot higher by 47.6% after rumors surfaced that it could be the next hepatitis C buyout target. As noted by CNBC reporter David Faber, there was a three-way bidding war for Idenix, so two other suitors wound up getting left out in the cold. Those suitors may be looking for redemption, and Achillion's pipeline might be the perfect target.

However, much like Idenix, I'd suggest you take out your 10-foot pole and ensure you get nowhere near these wholly clinical hepatitis C stocks as they're just plain frothy at these prices. Although Achillion does have four compounds currently in early and mid-stage clinical studies, its lead drug, sovaprevir, has been on clinical hold since last summer due to the discovery of phase 1 patients with raised ALT liver enzyme levels. Safety is a primary concern of the FDA, and both Idenix and Achillion's pipeline have produced investigational therapies with questionably safety records in the past. Until such time as Achillion can actually manage to get an investigational drug into late-stage trials I would strongly suggest keeping your distance.

Source: Randy Pertiet, Flickr.

Finally, and to stick with our theme of M&A today, Hittite Microwave (UNKNOWN:HITT.DL), a developer of integrated circuits, modules, and instrumentation for radio-frequency microwave and millimeterwave applications, soared 28.6% after agreeing to be acquired by Analog Devices (NASDAQ:ADI) for $78 per share, or approximately $2 billion. Analog Devices announced the deal earlier this morning and said it plans to finance it through a combination of cash on hand and short-term debt financing with an expected closing date in the late third quarter. Most importantly, the transaction is expected to be earnings accretive to Analog Devices adjusted EPS, which is what shareholders truly care about. Unlike the prior two stocks among today's top performers this deal makes sense to me. The businesses are indeed complementary to one another and Analog should see immediate benefits from the combination.